Add unit tests

[Daenyth]

Should run through basic usage with a prebuilt file list db.

[Daenyth]

One thing that might make this easier is to remove all the "print" statements from the search functions and instead have them return a data structure which gets passed to a print formatter in the main script, but could also be tested against with a stable database sample.

[jrstjohn]

If this issue is regarding pkgfile, then you can close this. Refer to #53.