glossary.rst: fix TODO comment markup

Commit b853ad906a2e0527e0313fb70d42137ae2d7aa11 added the sphinx
`glossary` directive, but it broke the TODO comments that were written
into the page. Indenting these multi-line comment blocks caused the
comment text after the first line of the block to bleed into the page.
Add initial Zebra tutorial

This includes set up instructions/references, as well as 1 complete
application tutorial (and the outline of 3 more).
zebra/tutorial.rst: add sysinfo and wordcount apps

There are actually two wordcount apps: wordcount and parallel wordcount.
Merge pull request #12 from larsbutler/fix-glossary-comments

glossary.rst: fix TODO comment markup which caused comments to show up in final page.
Merge pull request #13 from larsbutler/zebra-tutorial

Add initial Zebra tutorial
contributing.rst: fix a rst syntax warning
zebra/tutorial.rst: add sample apps 2-4

This includes `sysinfo`, `wordcount` and `map/reduce wordcount`.
Merge pull request #14 from larsbutler/zebra-tutorial-2

Zebra tutorial, part 2
zebra/tutorial: use real local TOCs

These are easier to maintain, though they might not look 100%
identical to the numbered lists they replace.
Merge pull request #15 from mgeisler/use-real-toc

zebra/tutorial: use real local TOCs
zebra/tutorial.rst: reorder `zpm deploy` cmd args

Reordered per this patch: https://github.com/zerovm/zpm/pull/112
contributing: recommend rebasing pull requests
contributing: describe how to reorder commits
contributing: add section on fixing your own mistakes
contributing: describe typical review cycle
contributing: section on one change per commit

This gives some advice on what not to mix into a single commit.
contributing: add section on writing good commit messages

This gives us something to refer people to in the future.
contributing: shuffle headings around

The "Contributing Guidelines" section is now more a section about how
to write good commits, so it has been renamed to better match its
content.

This means that we now have main headings about how to use pull
requests, how to write good commits and how to use the long-term
branches in the repositories.
contributing: remove C4 reference

Instead of referring to a large set of rules in an external document,
we now have sufficient guidelines in our own document to help
contributors. Our document emphasizes good code quality.

The rules and guidelines in our document are generic and have been
inspired by other large open source projects such as Mercurial, Git,
and OpenStack:

  http://mercurial.selenic.com/wiki/ContributingChanges
  https://github.com/git/git/blob/master/Documentation/SubmittingPatches
  https://wiki.openstack.org/wiki/GitCommitMessages

The idea is that this process should be familiar to other
contributors, while ensuring that we maintain high code and design
quality.
contributing: add link to contact page