Added missing classifiers to the `setup.py`

I have added extra topics:

```
+        'Topic :: Software Development :: Libraries :: Python Modules',
+        'Topic :: Internet :: WWW/HTTP',
+        'Topic :: Internet :: WWW/HTTP :: Dynamic Content',
```

Added information about framework:

```
'Framework :: Django',
'Framework :: Django :: 1.6',
'Framework :: Django :: 1.7',
'Framework :: Django :: 1.8',
'Framework :: Django :: 1.9',
```

And `python` versions:

```
        'Programming Language :: Python :: 2.7',
        ...
        'Programming Language :: Python :: 3.4',
        'Programming Language :: Python :: 3.5',
        'Programming Language :: Python :: Implementation :: PyPy',
```

I have also sorted the classifiers alphabetically.

Convert readthedocs links for their .org -> .io migration for hosted projects

As per [their blog post of the 27th April](https://blog.readthedocs.com/securing-subdomains/) ‘Securing subdomains’:

> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.

Test Plan: Manually visited all the links I’ve modified.

Make the JS wrapper configurable

Removed duplicate DISABLE_WRAPPER key in conf.py

Updated logger warnings

The outdated file checks in the compilers were using django storages to check
file existence and compare mtimes, but with my recent change (which restored
the older behavior of comparing the infile and outfile), these were operating
on absolute, local files, which could result in a SuspiciousFileOperation.

The compilers always operate on local files, so we can switch to using the
os.path methods for these instead. This is both more correct and more
efficient.

Link to RTD via HTTPS.

Split render_compressed in templatetags for easier subclassing

The base mixin for the template tags, PipelineMixin, performed the bulk
of its rendering logic in the render_compressed() method. It handled
both rendering output files (if PIPELINE_ENABLED was True), or source
files (if False). Due to the complexity of this method, it was difficult
for a subclass (which may need to perform more specialized logic) to
override this method without copying the code.

This splits out that function into two new utility methods,
render_compressed_sources() and render_compressed_output(). These take
the same arguments as render_compressed(), and are called by that method
as well. This allows a subclass to more easily replace the logic for
determining which to call, or to replace the logic for either of these
renders.

Add a view for collecting static files before serving them.

In a Django development setup, it's common to have a /static/ URL set up
to serve static media to the browser upon request. That's usually set to
either serve out of a specific directory or out of any configured
finders. However, the former doesn't guarantee any referenced files were
collected first, and the latter only considers source files (for the
purposes of timestamp calculation/caching) and not the
collected/compiled files.

This change introduces a new view, meant for use with Django's static
serving view, that will collect the referenced file before serving it,
guaranteeing that media like images and fonts are present.

To ensure that this view will return content quickly (especially
considering it will serve up any files referenced by the template tags),
an optimization was made to Collector to allow the caller to collect
only the given list of files. The view makes use of this to handle the
collection process fast.

Adds documentation regarding ES6 config

Included a comment regarding the required file extension of ES6, as this was not immediately obvious to me.

Fixes #550

Add error output for compiler errors within the browser.

Debugging CSS/JavaScript compilation errors can be difficult when viewed
within the context of a Django error page, and if there's a wider
problem with other CSS/JavaScript packages, they won't show up until the
first compilation error is fixed. This is worse if running in a mode
where Pipeline is running but Django error pages aren't being shown.

This change introduces an option, PIPELINE.SHOW_ERRORS_INLINE (now
enabled by default) that outputs any compilation errors at the top of
the page, visually distinguished from the rest of the page, and
containing information on the failing package, command line, and output.
This makes it much easier to debug what went wrong.

The errors are outputted into a hidden div, and then once the page has
fully loaded, they're placed at the top. This allows Pipeline usage
anywhere on the page to promote errors to the top, in the order in which
they're loaded. These also have a default style, but that can be
overridden (and in fact the whole error template overridden) by the
consuming application.

Add support for older Djangos

Support for 1.7 is pretty efortless after #536.
Support for 1.6 is more tricky and involves adding a missing class
(`modify_settings`).

rST wants underlines defining section names to be the same width as the text
above it. This trivial change cleans up those warnings when building the docs.

Add unit tests for the bundled compiler and compressor classes

If this environment variable is not set, multiprocessing throws a
NotImplementedError

Some nodejs executables set stdout and/or stderr to non-blocking, which
can trigger an IOError when the collectstatic command prints more than
1024 bytes at a time to stdout or stderr