Changes to allow edoc to run succesfully.

Added edoc-generated files that need to be deleted during <code>clean</code> to <code>rebar.config</code>. The <code>doc</code> target in the <code>Makefile</code> now depends on <code>all</code>, which includes getting dependencies and compiling. Fixed edoc errors in <code>riakc_datatype.erl</code> and <code>riakc_pb_socket.erl</code>