Coursera-dl

Features:
- Default arguments are loaded from `coursera-dl.conf` file
- Added option `--mathjax-cdn <MATHJAX_CDN>` to specify alternative MathJax CDN
- Added support for Resources section

Features:
- Add `--download-delay` option that adds a specified delay in seconds
before downloading next course. This is useful when downloading many
courses at once. Default value is 60 seconds.
- Add `--only-syllabus` option which is when activated, allows to skip
download of the course content. Only syllabus is parsed.
- Add support for `reflect` and `mcqReflect` question types in quizzes.
- Courses that encountered an error while parsing syllabus will be listed
in the end of the program execution, after all courses have been
processed (hopefully, downloaded). This helps skip vast output and easily
see which courses need user's attention, e.g. enrollment, session
switching or just patience until the course start date.

Bugfixes:
- Locked programming assignments in syllabus used to crash coursera-dl.
Now the script goes on parsing syllabus and skips locked assignments.
- Add missing import statement to playlist generation module

Features:
- Added option `--list-courses` to list currently enrolled courses (514)
- Added option `--jobs N` to download resources in N threads simultaneously (553)
- Added option `--download-quizzes` to download contents of graded and
ungraded quizzes (490)
- Added option `--cache-syllabus` to avoid downloading course syllabus on
every run (this option is rather for developers)

Bugfixes:
- Locked lectures are also requested from server now, which allows to
download some programming assignments that were not downloaded before (555)

Deletions:
- Support for old-style courses has been removed (Coursera discontinued old courses:
http://coursera.tumblr.com/post/145882467032/courseras-transition-to-a-new-technology-platform)
- `--ignore-http-errors` option has been removed and the default behavior
has been adjusted to include this option
- Removed deprecated `--on-demand` option. Now OnDemand classes are downloaded
by default

Bugfixes:
- When using `--process_local_page` option, errors downloading About
page will not stop course download
- Limit file name part to 200 characters and file extension part to 20
characters to alleviate "Filename is too long" issue

Features:
- Descriptions of assignments are saved in more cases (different courses
implement it in a different way)
- Images are embedded into descriptions of assignments and are available
offline locally
- MathJax is injected into descriptions of assignments to render math
locally (requires Internet connection)
- Add option `--ignore-http-errors` to ignore errors in internal
downloader during resource downloading stage
- Add option `--disable-url-skipping` to always try downloading
all the URLs that were found by the parser
- Add option `--downloader-arguments` (464)
- Add option `--version` (477)
- Better looking progress output: during the syllabus parsing stage
lecture/section names are printed in a hierarchical structure

Bugfixes:
- Stricter filename cleaning in on-demand course parser
- Better URL filtering
- Detect SSL errors and suggest link to the solution in the output
- Added workaround for "Filename is too long" on Windows