* was going to use to test duplicated content, but we're not supporting that for now

* New format: {tag}://{org}/{course}/{category}/{name}[@{revision}]
* Updated tests, code
* Added test chapter with : in url_name in toy course
* added test html page with : in url_name
* added a note to docs

* with backcompat location /grading_policy.json

* still backcompat with old mode

* apply policy per-course, even if multiple courses share course and org fields
* keep descriptors separate in xml store, so that if two such courses
  change the same module in different ways, it works.  Such edits will need to
  merged on CMS import...
* add get_instance(course_id, location) method to replace get_item(location).
  Update all the call sites
* tests, including a 2nd toy course with same course and org.

* course roots live in roots/{url_name}.xml
   - one is linked from course.xml

* policies live in policies/url_name.json
  - loaded based on course url_name

* Updated to pass policy through into xml parsing, so it takes effect
  before descriptor constructors are called.

* Update toy test course to new structure, fix up tests

- add 'type' and 'points' to capa_module metadata
- replace old 'title' tag with display_name

TODO:
* need unique slugs for errors so they don't overwrite each other on export.
  - try to preserve origin slug.  If not possible, generate random one.

* figure out what metadata to strip.  e.g.
 ({'data': '<problem><p><h1>Finger Exercise 1...'},
    {'data': '<problem points="1" type="lecture"><p><h1>Finger Exercise 1...'},
    False)
  - where did points and type come from?  Do we want them there?


* separate broken and non-broken test courses

* add course and org to full/course.xml
* fix error path in clean_xml script
* commit rakefile change needed by c5334f150c

* Add extra nested html file
* add a start date

* More tests for mongo modulestore, including tweaks to test files
* add location_to_id method to CourseDescriptors
* Implement path_to_location method in mongo.py
  - TODO: does not handle position in sequences yet.
* fix bug in jump_to view.

* Clean up test data for simple, toy courses
* clean up test_mongo.py
* write initial test for path_to_location
* hook up view to use path_to_location

Next: actually implement it :)

* fix up toy course to match current format
* fix github sync test that referred to toy course

* change custom tags in test/data/full to new single-tag format
* fix broken file references
* fix argument to import_from_xml
* error_handler fix in mongo.py in next commit

Add tests for the edit page for the toy course, and make sure that exporting to github sets up the git repo properly