Rename ComrakFoo types to just Foo for easier usage

[tgross35]

There are a few types whose names start with Comrak:

ComrakExtensionOptions
ComrakOptions
ComrakParseOptions
ComrakPlugins
ComrakRenderOptions
ComrakRenderPlugins

This sort of naming is somewhat redundant - they are longer & clunky to work with, even though they are unlikely to conflict with anything. This PR removes the Comrak prefix so they are more ergonomic. Any users who do have conflicts can use e.g. comrak::Plugins.

This PR also adds aliases for the old type names, so no workflows are affected.

[kivikakk]

Thanks, this is a very tidy change. I'll merge it when I'm next on the project!

[kivikakk]

A reminder to me to fix this up pre-merge and do another once-over.

Suggested change

	// Update the "comrak --help" text in 's own README.
	// Update the "comrak --help" text in Comrak's own README.

[tgross35]

Thanks!