Refactor fdoc_to_html

[ohrite]

Most modern Ruby CLI apps use Thor to build out their frontend. Thor provides a lot of nice messaging and convenience for building a generator. Given that fdoc has a CLI and it's a generator, this seems like a great fit!

The important bits:

• Renamed the executable from fdoc_to_html to fdoc, with a single action called convert
• Split the url base path parameter into an optional flag called -u/--url-base-path
• Split the output path parameter into an optional flag called -o/--output
• Default the output base path to ../html based on normal usage, so for docs/fdoc it generates docs/html

[zachmargolis]

Thanks for adding this!

This is an API-breaking change so we probably want to bump the minor version, add something to gem announce for deprecation, and then leave something in fdoc_to_html that proxies to the new one (also with a deprecation warning).

[ohrite]

Oh, good point! I'll add in a proxy now.

[zachmargolis]

Going to merge this, then add the deprecation warning, version bump myself. Thanks!