Add Pre-processing of HyperMake files

[easeway]

Introducing a template language (most likely the Go template) for pre-processing HyperMake file (as well as .hmake/.hmakerc files).

Add command line option -D key=val and normal arguments in the form KEY=VAL to provide context for pre-processing.

E.g.

hmake -D PLATFORM=linux target1 target2 OS=linux ARCH=arm

is equivalent to

hmake -D PLATFORM=linux -D OS=linux -D ARCH=arm