Adding support for --force-ext option.

Allows the user to specify an extension on the commandline. When
present, all input files will be processed as if they have this
extension.
Update src/docco.coffee to support .md output as an option

Added support to optionally produce markdown files in addition to html.
Update resources/docco.jst

Adding an optional second output type required the destionation()
method to have a second argument for the extension.
Update test/tests.coffee

Added a new test case for markdown_output and adjusted the expected var
in the testDoccoRun method to account for the extra file in this test
case.
Update README

Added the new -m option to the README
Forgot to 'cake build' before submitting my pull request.  Noticed this when I installed this now docco locally and tried to use it.
Merge remote-tracking branch 'remotes/danielmlipton/master': add MarkDown (-m) output option -- fixed the option parsing of -m at the same time as merging the code. (refer to defaults.markdown and make it a boolean)

Conflicts:
	lib/docco.js
	src/docco.coffee
Merge remote-tracking branch 'remotes/MaxPower15/force-ext': --force-ext is useful when running Makefiles, etc. through docco.

Conflicts:
	README
	lib/docco.js
	src/docco.coffee