Split out static library

[jcrist]

The libpython static library is quite large

$ du -h ./lib/libpython3.7m.a
 16M    ./lib/libpython3.7m.a

and won't be used by most users. It would be useful to split this out into a separate package if possible, to reduce installation size (important for docker images).

[mingwandroid]

Good idea. We should add a split package for the testsuite too (which we delete at present!)