functional reorganization

Organize the files functionally:
- kmod/core: core kmod source
- kmod/patch: patch kmod source
- kpatch: kpatch script
- kpatch-build: kpatch build script and supporting tools
- contrib: distro-related files
compressed cache

Saves about 2G disk space per kernel version
clarify that kpatch should work on non-Fedora
use consistent naming for core and patch modules