Documentation revisions, mostly in Installation Instructions

[ttmc]

• Deleted test.rst (not needed anymore)
• Moved the contributing, faq, and release-notes sections to the end
• Fleshed out the release-notes section
• Substantial changes to the Installation Instructions. I tested them on Ubuntu 14.04. @r-marques please check:
  • Linked to RethinkDB Server installation instructions for all OSes, rather than giving them for Ubuntu and no other OS. That way users always get the latest instructions for installing RethinkDB Server.
  • Added that Python 3.4+ is required, and a link to get it
  • Rearranged the section on Installing and Running BigchainDB. Added instructions for installing OS-level dependencies on Ubuntu 14.04. Moved the "Run BigchainDB" instructions to the end (after installing BigchainDB).
  • Copy editing

[codecov-io]

Current coverage is 67.56%

Merging #26 into develop will not affect coverage as of 9a7a703

@@            develop     #26   diff @@
=======================================
  Files            14      14       
  Stmts           746     746       
  Branches          0       0       
  Methods           0       0       
=======================================
  Hit             504     504       
  Partial           0       0       
  Missed          242     242       

Review entire Coverage Diff as of 9a7a703

Powered by Codecov. Updated on successful CI builds.

[ttmc]

I'm going to merge it now, because I want the improved installation instructions to go live as soon as possible. If you spot errors, or have suggested changes, then edits can be made in a future PR.