Add 32-bit launcher

For #7, HostBitness input for AssemblyArgument to select the target
bitness for the child process. The launcher EXE is only required for
running 32-bit child process on a 64-bit OS. It doesn't need to be
referenced by the calling assembly, but does need to be on the load
path.
Update readme and changes

Also fixed test settings after having changed the output directory for
the launcher and no longer trigger a breakpoint in debug builds of
AssemblyHost.
Rename CHANGES to changelog
Add missing license text
Merge pull request #13 from spanglerco/32-bit-launcher

32 bit launcher