This brings together the two libraries back into one now that the whole
design is pretty well sorted out. They depend on roughly the same libraries
anyway and it's way easier of the single library can both read and write
the capture files (along with bringing in libsysprof-capture symbols in
a single place).
This requires that things use #include <sysprof.h> now instead
of individual includes. A few cases are still allowed in the
libsysprof-capture library to make copy/paste embedding easier.
As we gain in usage, we need to be more careful about using a prefix
that will not collide with other symbols. So version 3 of our ABI will
change to using Sysprof/SYSPROF/sysprof as the various prefixes.
The soname/api version bump will happen later on this branch so that
things are easier to test up until then.
