Clk2clock - rename the implicit "clk" module input "clock" (#387)

* Rename implict module "clk" input to "clock".
This doesn't rename all the "self-contained" test instances.
nor the memory "clk" enables,
nor the implict module "clk"s in the regress .fir files.

* Consistency: rename implict module "clk" input to "clock" in "self-contained" test instances.
This doesn't rename the memory "clk" enables, nor the implict module "clk"s in the regress .fir files.