Added a link to the list of all tz database time zones
Fix Post#url escape

Post#url was escaped using CGI.escape.
When file name contains a space character, its url points to
non-existing URL.

For example, when we have a post named '2014-01-02-foo bar.md',
we expect its url to be '/2014/01/02/foo%20bar.html',
but it was actually '/2014/01/02/foo+bar.html'.

We now define Jekyll::URL.escape_path and Jekyll::URL.unescape_path,
and use them to escape and unescape Post#url
Fix Page#url escape

Post#url wasn't escaped at all.

For example, when we have a page named 'a#b.html',
we expect its url to be 'a%23b.html',
but it was actually 'a#b.html'.

We now use Jekyll::URL.escape_path and Jekyll::URL.unescape_path.
Move URL escape to Jekyll::URL
Add links to our lovely new Help repo
Link to Docs should always be 'Docs'. Props @cobyism
Shorten 'Overview' to 'Home'
Clean up fonts used.

* remove the unused ones
* switch to using `700` for `bold` consistently
* use `400` for normal font weight
Switch to using an ico file.

Works in all browsers plus it includes a 32x32 icon alongside with the 16x16 one.
Extract plugin management into its own class.
Redirect all the people to the help repo.
Require 'plugin_manager' in lib/jekyll.rb
remove default post with invalid date
Merge pull request #2200 from fabianrbz/remove_unnecessary_post
Update history to reflect merge of #2200 [ci skip]
With 5 items in the main navigation, limit the width to 20% rather than 25%.
Restore 'Documentation' ~> 'Docs' because long words are fun.
Merge pull request #2177 from jekyll/help
Update history to reflect merge of #2177 [ci skip]
Merge pull request #2193 from XhmikosR/docs-favicon