Change mu_assert return type to int

Instead of displaying the error message when in mu_run_test, it was
decided that might as well display when it occurred, namely in
mu_assert. This in turn enables one to display the function name and
line number if a failed assert were to occur, making debugging easier.
Update README
Merge branch 'master' of github.com:chutsu/munit

Conflicts:
	README.md