Changes nim_file_to_html into parametrized procs. Refs #22.
Wraps source_file_to_html and related for the C API. Refs #22.
Renames test since the proc is generic now. Refs #22.
Adds highlight test of other sources. Refs #22.
Adds file extension to title of generated HTML. Refs #22.
Adds memory render test without automatic title. Refs #22.
Changes source transform to use code directive. Refs #22.

The code-block extended directive was applying nimrod syntax
highlighting to unknown source style.
Wraps code blocks in prismjs' language style. Refs #22.

When the prism code is included the line numbers won't have different
font sizes and hopefully both table cells with match the height.
Adds minor changes to lhighlight module to match stdlib. Refs #22.
Removes nimrod language name from code-blocks. Refs #22.

It was unneeded since the default language is already nimrod, and it is
troublesome with the compiler name transition.
Documents task in changes log. Refs #22.
Merge branch 'feature/t22_generalize_source_highlighter'