security/libsparkcrypto: Optionally generate documentation
It was not possible to generate libsparkcrypto documentation before the
textproc/adabrowse port was created. Now that AdaBrowse is available,
add a "DOCS" options to generate the documentation.
While here, convert USE_GMAKE to USES+=gmake and fix DESTDIR to work
properly instead of installing during the build phase. The Makefile
also had to altered to install the documentation as well.
Approved by: bapt (mentor)