Docs/Makefile Improvements

Added some notes and stale messages that tripped me up as a new user.
Converted the stdlib compilation over to a makefile. Tested on Linux only but
OSX should work too.

If `EXT_LLVM_DIR` isn't set, `all.make` now tells you so.

Running `./stdlib.bash` wil now print a friendly usage message telling you how to
clean or build core/extra/all libs and also how to compile specific libs only using 
command line arguments.

To keep the makefile more concise It doesn't handle dependencies between the libs,
But hat should be ok.