This also moves stackstash.[ch] into a location that can be
embedded by both the libsysprof and libsysprof-ui code. We
pass native pointers to the structure as a gpointer in the
public API to allow for this. The performance of that code is
incredibly sensitive to the interactivity of Sysprof.
The big thing going on here is that we are going to split up the libraries
a bit better, and remove GObject from the capture library. The libsysprof
library will bring in the capture library statically, so we can export the
symbols we want.
Eventually, we will bump the version to sysprof-3, but not yet.
