Merge #57

57: Add mcounteren.rs, cycle[h].rs, instret[h].rs, and update mod.rs r=Disasm a=dkhayes117

I'm not sure the set_clear_csr!() macros are correct in mcounteren.rs.  I get a build error that says `cannot find function `_clear` in this scope`

Co-authored-by: dkhayes117 <dkhayes117@yahoo.com>