simplify the command-line api

I remembered why I wanted this! It makes things a lot easier to read and to type. xargs + find isn't a good solution, because it's non-portable (find works slightly differently on different unixes)

There are 3 major changes here:
- support for file globs
- support for -O=ADVANCED
- support for -W=VERBOSE

Based on feedback from the last PR, I added better docs on how to use this, and got rid of the gcc-style O=2