Change source map option from -g to -m or --sourcemap.
Add --load-path as alias for -I.
Add --style as alias for -t.
Add --line-numbers and --line-comments as aliases for -l.
Add --help as alias for -h.
Change input/output behavior to be similar to sass (Ruby).

- When no parameters are given, the input is read from stdin and the
  output is printed to stdout.
- When 1 parameter is given, it is interpreted as input path and the
  output is printed to stdout.
- When 2 parameters are given, the first one is used as input path and
  the second one is used as output path.
- When more than 2 parameters are provided, an error message is printed.
Merge pull request #44 from svnieuw/interface_rework

Change sassc interface to be more similar like Ruby sass.