add documentation for registration REST API
api.txt - just reformatting

break the very long lines
updated REST API documentation

(fixed typos, better wording)
removed some data from reg-parameters_required.xml example

to make is shorter
put a separator between the permissions

(so the rendered HTML looks better)
build the REST documentation during RPM build
Merge pull request #54 from webyast/restdoc_for_registration

add documentation for registration REST API