docs 5.x-1.0-alpha2

The second alpha version of this module changes the default file upload form to support only one file attachment per node. It makes more sense and makes the form validation much easier. This revision has a bunch of bugfixes and associated code cleanup and refactoring.

Unfortunately, at the moment once uploaded, the file stays untouched. I'm considering to maybe do an add-on module, which will provide the file revisions UI. This is done to keep the module as simple as possible, and the default upload form is designed for a different workflow.