Rather than directly invoke command-line Python (and Mako) from the
assets Rakefile, or call an external Python script, use a Django
management command to preprocess all asset template files.

An "asset template file" is defined as a static asset file with a
file extension indicating that it needs to be run through a template
engine prior to Sass/CoffeeScript compilation or packaging with other
assets. The preprocess_assets management command will look through
all of the files listed in the `STATICFILES_DIRS`, preprocessing each
as needed. Preprocessing strips off the special template file
extension, creating a new file in the process.

Currently, the only variable accessible in an asset template file is
the `THEME_NAME`, defined in the settings.

Updated documentation in doc and README and made some small edits to bash script for added robustness

Added documenntation to the docs folder and edited the mac bash script in response to tests

Use MITX_FEATURES to tell if we're in the CMS; this is much cleaner. Also use $.data instead of a hidden div.

Give all response types an id attribute.  CustomResponse had one, with a silly name.  Use it for all ResponseTypes.

Give all response types an id attribute.  CustomResponse had one, with a silly name.  Use it for all ResponseTypes.