GXemul Code2

Unbreak build; the UNITTESTS(className) case is special (used in GXemul.cc).

Oops, MIPS PROM is of course at physical 0x1fc00000, not 0xffffffffbfc00000. :-)

Updating Doxygen class comment for MainbusComponent: child components should be MemoryMappedComponents.

Adding some TODOs about automated documentation generation.

Minor updates to the Doxygen class comment for MemoryMappedComponent, and to the Source code documentation Main Page.

Minor documentation fix.

Adding a MemoryMappedComponent base class, which all memory-
mapped components should inherit. (The canonical example is
the RAMComponent class.)

The MainBusComponent can now forward reads and writes to
memory-mapped child components.

Make parsing of hexadecimal values actually work. (It was never tested before, and was broken.)

Adding ROM (actually RAM :-) to the testmips machine, at 0xffffffffbfc00000.

Continuing on mainbus related things; moving the mips_cpu in the testmips machine so that it is placed on the mainbus.