FreeBSD support, arch aliases, full config tree merging

FreeBSD support and config compilation (#15)

* Added support for FreeBSD

* Added darwin -> macos aliases

* Fleshed out arch/os aliases, normalize targets always

* Added aliases for FreeBSD/OSX uname -m arch

* Try harder to divine branch when github lies to us

* Always normalize toolchain platform

* Install docker in ubuntu image for cross compile

* Make sanity tests check for platform normalization via armv8

* Make sure compiler installation happens at package installation time

* Fixed where path shenanigans

* Finally got the courage to just recursively process config trees

* Resolve symlinks when looking up executables