Glasgow Embedded / Glasgow - History

applet: metaclass improvements for abstract applet base classes.

* Make GlasgowAppletMeta inherit from ABCMeta.
* Make build() and run() abstract methods.
* Allow inheriting from GlasgowApplet without specifying a name.
This results in an abstract applet, which is not registered in
the applet database, and can be used to provide shared functions
to other applets (usually, the interactive frontend).

applet.memory.prom: encourage (sic) metastability during reads.

This change is tested with Atmel AT29C flash and may or may not have
any effect on other memories. In case of this Atmel flash, output
buffers have parasitic feedback (likely through power supply) and
will oscillate if encouraged, e.g. if OE is kept asserted, or if data
transitions are maximized.

applet.memory.prom: s/histogram/popcount/ in commands.

applet.memory.prom: fix DIV/0 in histogram for perfect flash.

applet.memory.prom: add `atmel write` command.

Also, make queueing actually work by escaping the RUN command if it
happens to occur inside the buffered block.

applet.memory.prom: add health histogram command.

With the accompanying tool.