Added optional flag to firmware

![screenshot 2014-03-03 18 20 00](https://f.cloud.github.com/assets/1721040/2316226/f5d96af4-a32f-11e3-9d7b-46be01cc1813.png)
Sorry about the styling problems, tried to match everything but I kept screwing up.

As for the info files, they should follow this convention for now
```
# Notes
#notes = "note1|note2|note3 with spaces|note 4 with spaces|note 5 (test)|note6"

# The number of mandatory/optional firmware files the core needs
# firmware_count = 7

# Firmware entries should be named from 0
# Firmware description
# firmware0_desc = "filename (Description)" ex: firmware0_desc = "bios.gg (GameGear BIOS)"
# Firmware path
# firmware0_path = "filename.ext" ex: firmware0_path = "bios.gg"
# Is firmware optional or not, if not defined RetroArch will assume it is required
# firmware0_opt = "true/false"
```