Added functionality

[AllanLRH]

Hi, I really enjoy using the plugin, and have added some functionality which I missed :)

It's described in the README, so I won't repeat it here in too many words, but basically it adds:

1. Insertion of "date", "time" and "date time" (European formatted date: day/month/year)
2. Computation of sha1 and md5 checksums
3. Formatting of numbers (floats)
4. Imports the collections.Counter class
5. Add some convenience functions for set operations

[vim-zz]

Thanks Allan this is awesome. I have merged and pushed as a new tag, so it should be deployed anytime