Initial release

Markdown transclusion utility supporting:

- **whitespace sensitivity**
  If the transclude is only prefixed by whitespace, the whitespace will be added to every line in the transcluded document, indenting the transcluded content.
- **paramaterized transcludes**
  Sometimes when you may want to transclude a file that may need to have additional content injected into it. Parameters allow you to specify an injection point, in the file which will be transcluded. The injection point will allow the parent to specify the file to be transcluded into the injection point.

I'd avoid using `parameters` for two different things.
`for [placeholder, filename] in (p.split ":" for p in parameters)`