Implement first thread spawner version.

Compiles to decent RTL. Tests does not pass.
Rename and tweak thread spawner
Fix errors in thread spawner test bench
Fix thread spawners for thread numbers i*barrel_height*num_sp
Fix tb, and cleanup
Merge pull request #30 from dmpro2014/thread_spawner_impl

Thread spawner impl
Add decode support for add immediate
Merge pull request #31 from dmpro2014/decode_fix

Add decode support for add immediate
Improve constants file
Fix broken testbenches