Made Makefile more configurable.

Moved user configurable vars to Makefile.conf.template. User can
overwrite configuration variables by setting them in Makefile.conf.
Added printconf target to show build config.
Setting defaults based on current platform (uname -s).
Checking if command can be executed using 'command -v X'. "test -x CMD"
checks only whether a filepath is executable, but doesn't work for
simple commands.

Conflicts:
	Makefile