GXemul Code2

Importing opcodes_mips.h from GXemul 0.4.6.3.

Links are now generated from component names in machines.html
to corresponding component_xxx.html pages.

The ListComponents command now shows the short description of each command.

Introducing "visible class names" in addition to the normal
class name, for components. This makes mips_cpu0 show up as
just cpu0, which is much nicer.
uint16_t, 32_t, and 64_t state variables are now outputted in
hexadecimal form in ToString(), for readability.

Adding a comment about "component paths" to the source code documentain main page.

Adding a section about Model-View-Controller to the source
code documentation main page, and a simple picture of what
the component tree may look like.

Adding a unit test for doubles in StateVariable::SetValue, for values such as 1e-100.

Some more work on the GTKMM GUI: the debug output window now
shows debug messages and commands being executed.

Instead of loading binaries into an AddressDataBus, they are
now loaded into a Component, which, if it has a "pc" state
variable, is set to the entry point. Starting gxemul with
-E testmips test/FileLoader_ELF_MIPS actually attempts to
start running the binary now :-)

Catching std::exception at the outermost level, in order to
print a reasonable message if the application crashes.