add get_writer signal and unify with get_generators

Fix outdated docs of get_generators to unify.
Merge pull request #1330 from smartass101/unify-run-get_-signals

Add get_writer signal and unify with get_generators
Fix #1311 wide tables in RTD theme, remove old theme files

This works by adding a CSS overrides file to the Sphinx app stylesheets.
Really fix #1311 by declaring CSS overrides as !important

this is needed because on RTD the common hosted theme stylesheets get added
after the overrides.
Fix #1277 use rsync -c option as all output is rewritten

Because Pelican always rewrites all output, the mtimes always change, so
rsync would always transfer all the files which defeats the purpose of
rsync. The '-c' option (--checksum) compares the checksums rather than
mtimes.
Add Python 3.4 to Travic CI configuration
Show setting defaults as actual code

For some reason, setting names on the Settings page have long been
wrapped in single back-ticks (usually meant for linking in reST) instead
of double back-ticks (meant for denoting code). This seems to be
widespread throughout the docs, and it's not clear if this is
intentional or simply a reST formatting error that got propagated by
others in order to stay consistent. This commit applies double
back-ticks in any case where something resembling code is shown, with
the idea that single back-ticks should only be used when linking.

More importantly, the settings denoted their default values in
parentheses, which hapless users often included when copying and pasting
these values into their config files. As one can imagine, confusion —
not hilarity — ensued. Setting defaults are now shown as they would
actually appear in one's settings file, with an equal sign and without
parentheses.

During this spelunking expedition, many other minor improvements were
concurrently conducted.
Remove errant leading spaces from fabfile.py.in