Added DMD support and a nicer makefile

Added set-dmd.cpp with Diamond Coin support.
Refactored makefile for single target support, if no target specified or  `all`, all targets are compiled.
All targets: `make`, `make all`
Selected target(s): `make dmd`, `make str`, `make dmd str`, etc...
Refactored makefile to add clean target.
`make clean`