Add Flags section to package view (refs #66)

See #66 for more info. Uses the already existing flag information from the general package description and prints out a table of flags, if there are any, with a little tip about how to enable/disable flags. Example from the `jack` package:

![flags](https://f.cloud.github.com/assets/11019/1649607/224b7406-5a15-11e3-86d1-1d5b5e068426.png)