I just created a makefile so that mruby can still be build by the "normal unix method" make, make test, make clean. I of course only call minirake.
Add makefile for backward compatibility of shell build processes.
update INSTALL document based on #650; according to #651
It's better to be RAKE = ruby ./minirake for windows.
RAKE = ruby ./minirake
Indeed. fixed by 4b19fd9