Update gist.rb comments only

Strictly updated the reference to Examples and Valid Syntax to be inline with jekyll/jekyll-help#32
Merge pull request #1 from iamgabeortiz/gist.rb-doc-update

Update gist.rb comments only
Merge pull request #2326 from iamgabeortiz/master
Update history to reflect merge of #2326 [ci skip]
Fix site template permalink typo
Merge pull request #2331 from albertogg/fix-site-template-permalink
Update history to reflect merge of #2331 [ci skip]
Don't fail if any of the path objects are nil.

Fixes #2325
Update history to reflect the closing of #2325.
add missing 'as'
Register subclasses of subclasses of Jekyll::Plugin

The Sass and SCSS converters are practically the same – only different in
the input syntax and file extension. As such, we've created
`Jekyll::Converters::Scss` which is a subclass of `Jekyll::Converter`, and
`Jekyll::Converters::Sass` which is a subclass of
`Jekyll::Converters::Scss`. When `Site#instantiate_classes` is called on
`Jekyll::Converter`, it only instantiates the `Scss` converter, not the
`Sass` converter. This change fixes that.

Fixes #2334.
Update history to reflect fixing of #2334.
Merge pull request #2337 from sankage/grammar-slam
Update history to reflect merge of #2337 [ci skip]
Update site history.
Use site.title instead of site.name in site template

Fixes #2324.
Update history to reflect the closing of #2324.
Require mercenary v0.3.3 or greater (below v0.4.0)
If the input is a string but Time.parse can't parse it, maybe it's a UNIX timestamp.

Fixes #2339
Update history to reflect the closing of #2339.