Added $sr, $dffsr and $dlatch cell types
Added $_SR_[PN][PN]_, $_DFFSR_[PN][PN][PN]_, $_DLATCH_[PN]_
Added techmap rules for $sr, $dffsr and $dlatch
Bugfix in dffsr techmap rules
Added RTLIL NEW_WIRE macro
Added dffsr support to proc_dff pass
Changed NEW_WIRE API to return the wire, not the signal