post_url tag raises ArgumentError for invalid name

Using post_url tag with invalid name raises TypeError.

It should raise ArgumentError and should display detail of the error to
fix the error.
added error description for invalid post name
Default Maruku fenced_code_blocks to ON.

Extends https://github.com/jekyll/jekyll/pull/1799
Add two tests for Maruku fenced code blocks
made error description more helpful
variables in include tag with filters
refactor file+matter creation in cucumber steps
refactor step to support page creation
add failing test for sorting pages by custom variables
clean up custom variable sort feature
removed duplicate test scenario
edited raise message when validating included file
edited documentation for include tag
Add in 1.4.1 and 1.4.2 changelog
allow data attribute access by Liquid on Convertible items
make non-data properties/methods accessible to Liquid

per https://github.com/jekyll/jekyll/pull/1849/files#r8490593
Fix the highlight tag feature

Previously, the assertion made wasn't enough to check whether the code
block was correctly parsed through Pygments (and it was not the case).
This commit simply ensure there is a div with the "highlight" class and
fix the test to correctly invoke the Liquid tag rendering.
Rename the pygments option to highlighter

Rename the pygments configuration option to highlighter to allow
different highlighters in the future. For now, the allowed values are
`pygments` and `null`.

It's now more straightforward to plug another syntax highlighter.
Add support for the Rouge syntax highlighter

By setting the `highlighter` setting to `rouge` you can now easily
highlight your code with it instead of relying on Pygments. However,
Jekyll doesn't depend on Rouge explicitly, you will need to install it
or add it to your Gemfile.

The documentation has been updated accordingly.
Set highlighter to pygments when upgrading

In case you are upgrading from 1.4.2 to 2.0 and the pygments option is
set to true, then the highlighter option will be set to pygments
automatically.