textproc/adabrowse: switch build to .gpr to avoid ASIS rebuilds
At least with the upcoming gcc49 and ASIS 2013, I've been seeing gmake
Makefile-based builds trying to rebuild ASIS rather than just use the
provided static library. I don't know what causes that, but I did notice
that it doesn't happen with GNAT project files.
1) Disregard gmake completely and provide a new build.gpr file
This will work when gcc-aux is moved to gcc49.
2) Add DOCS option and install the html documentation optionally
3) Relocate LICENSE to make portlint happy
4) Using GPR makes this jobs safe (although the job number might be
limited to 1 anyway in this case)