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
Better error message when time is not parseable

Give the full path of the file that cannot be parsed so the user can locate it easier. Follow up the error message with helpful instructions: they can resolve the error by fixing the date or excluding the file or directory from being processed.
Sort pages by name by default

The order that files are returned differs across operating systems, so
ensure that they're being sorted after the fact.
link to Stack Overflow answer re: Dir sorting
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
clarify page sorting test
Merge pull request #1848 from afeld/sort-pages
Update history to reflect merge of #1848
Add in 1.4.1 and 1.4.2 changelog