Change Pulldown so it doesn't need to be instantiated with new

No need for it to be a "class", so just made it a plain old boring
object. Much less overhead now, no need to call new Pulldown().init(),
just pulldown.init;

Renamed module from Pulldown -> pulldown.

Updated the CLI module and the tests to use the new way.

Deleted the files in lib, just put the source into the main file to keep
it tidy.
update docs to match new pulldown structure
Refactor the CLI object so it doesn't need to be instatiated with new
Merge pull request #79 from jackfranklin/no_new_needed

Remove need for constructing with new keyword.