Change sassc interface to be more similar like Ruby sass.

This pull request changes the `sassc` to behave more like `sass`:

- Aliases are added for `-I` (`--load-path`), `-t` (`--style`), `-l` (`--line-numbers` and `--line-comments`) and `-h` (`--help`)
- The `-g` option has been replaced by `-m` and `--sourcemap`.
- The `-o` option is removed. You can specify the output file as a second parameter just like `sass`. For reading from stdin the flags `-s` or `--stdin` are introduced.

This should solve issue #42.