doc: Add FAQ

This patch introduces a new FAQ, and adds some FAQ-like info inline
to doctrings where appropriate. NOTES.md is no longer necessary now
that we have its content properly documented, and so it was removed.
doc(README): Note Python 3.4 support
refactor(util.misc): Remove deprecated functions

Removes percent_escape and percent_unescape, which were deprecated in
0.1.8.
doc: Fixup falcon.util namespaces for misc
chore: Make Travis less chatty on IRC
doc(FAQ): Address authentication question
doc: Add 0.1.8 highlights under "Resources"
doc: Add community guide

This patch introduces new "help" and "contribute" pages, and combines
them with the existing FAQ under a new "Community Guide" section.

Partially-implements issue #112
Merge pull request #257 from kgriffs/master

doc: Add community guide
doc: Copy note about installing under OS X to sphinx docs

This note was previously only in the README. Copy to sphinx so
it will show up on RTD as well.
doc(StartResponseMock): Fix attributes docstring
Merge pull request #258 from kgriffs/doc

doc: Copy note about installing under OS X to sphinx docs
add app-context properties to Request and Response

Provide properties for application developers to use for app-specific
context data that doesn't fit well into req.env or resp.{body,data}.