Some more fixes / cleanup to the Makefile.

Removed some more targets.
Removed multiple messages about $RUST_PATH and show them all at the top
of the Makefile.
Rename to `Makefile` which is more standard than makefile.
Don't include the `$RUST_PATH/mk/crates.mk` file if $RUST_PATH is not
defined.
Merge pull request #22 from am0d/makefile

Some more fixes / cleanup to the Makefile.
Update Makefile for Travis