Improve robustness of check_hw rule
Makefile improvements

Go a bit mad on testcase refactoring
Lockfile for builds of demos

Hoist locking

Prevent premature creating of temp dirs

Improve `zip` and `gzip` dist rules
Rewrite OFFSET in BlockRAM for Quartus

Apparently Quartus can compile a ram with a non-zero base, but the subsequently
generated memory initialisation file is rejected because something thinks the
resulting RAM ends at SIZE instead of at (SIZE + OFFSET).
Update to Quartus 13.1, Cyclone III

Specify DE0 device ; I am more likely to be using a DE0 board to prototype with
Quartus.

Remove references to obsolete files
Mend clock issues

The clk_core0 must be a register

Add preliminary clock constraints
Ignore Quartus-generated backups

Ignore more generated files

Ignore / clobber simulation files
New Makefile

Based on `quartus_map --help=makefiles` but unrecognisable.

May need some corrections if the `*.chg` files in that recommendation imply
some weakness in how the `*.???.rpt` files are generated.