Command-line usage

[davidweichiang]

In general I suggest making the usage look more like gcc...

• [x] Make source an argument rather than stdin
• [x] -o for output file
• [x] -O1 for optimization
• [x] I'm not used to Y/N options but I am not sure what to suggest instead

[davidweichiang]

• [ ] don't allow multiple options if they don't make sense (e.g., input files, -o)