Pull in, simplify, and bump the libmirage exheres.

Note that this version *will not* work with cdemu unless cdemu is bumped to
at least version 2.0.0; I've added a blocker so people are aware of
this.
Add dev-libs category for libmirage
Rewrite libmirage exheres to use new cmake build system.

Annoyingly, it uses non-standard option formats...
libmirage: Whoops, forgot category on gobject-introspection
libmirage: Fix call to cmake_simple_option
libmirage: Add missing libsamplerate dep
Merge branch 'master' of github.com:kepstin/kepstin-exheres