Seems friendlier to return a Date object rather than a formatted string,
so the consumer can decide what to do with it.
Use 'require_relative' rather than 'require' so that consumers don't
have to fuss with the library path.
QIF uses a single colon between names in the account hierarchy, rather
than two colons (e.g.
http://en.wikipedia.org/wiki/Quicken_Interchange_Format).
Merge branch 'colon'
Merge branch 'date'