Add a section on pickling
Merge pull request #1 from khinsen/multiprocessing

Add a section on pickling
Fixed grammatical typo
Merge branch 'fix-402' of github.com:r-gaia-cs/bc into fixing-missing-plots
1.  Merging fixes for missing image files from @r-gaia-cs.
2.  Putting IPython Notebook stuff in a separate Makefile so it won't inadvertently trigger when doing a regular site build.
    This ensures that people who *don't* have IPython installed,
    and don't want to re-create the Markdown files for notebooks,
    won't accidentally try to do it.
Updating documentation on build process
Updating contribution guidelines based on feedback from @r-gaia-cs
New Makefile holding IPython Notebook conversion rules
1.  Refactoring code to allow for optional fields.
2.  Making `enddate` optional.
3.  Adding optional `eventbrite` field check.
4.  Adding always-pass checks for `venue` and `address` fields for completeness.
5.  Adding tests for the above.
Removing setup images only used in old lesson material
Added link to doit documentation
Put the proper documentation for doitmagic.py
Added some information about the benefits of doit vs. Make
Generate .html files for all parts of the doit lesson
Changed the order in which parallel code is described to begin with
defining the work to be done (which follows the order in the complete
example source code)
Avoiding confusing terminology
Resetting unintended changes
Tell people what to type into the mars.txt file.
Copy git lesson files as basis for hg lesson.
Port index and intro pages to hg.