DSP48E1 support, Spartan7 support
- Support DSP48E1 hardware multipliers, including cascaded hardware multipliers. It is not feature complete, but now should handle most of portable verilog that is inferred by Yosys.
- Added Spartan7 support
- Now router1 is the default router, because router2 has problems routing DSP blocks. It still might work on some designs, though.