Solution: establish a matrix of CI options. On one axis we have the
build system (autotools, cmake, android) and on the other axis we
have the encryption options (tweetnacl, libsodium or none).

Solution: checkout stable branch before building

Solution: use --without-docs (changed from --without-documentation)
and also --quiet.

Solution: use parallel make (-j 4) and don't build man pages.

Solution: add `--depth 1` parameter to `git clone` commands

Solution: rename to simple builds/android.