Fixes UUID Timestamp, also adds FromTime function

Fixes bug where nanoseconds were not being pulled out of the 60-bit
UUID time correctly. Cleans up that code to use timeBase rather than a
special hex value.

Also adds FromTime function to generate Type 1 UUIDs from arbitrary
times.
Re-use UUID package for Timeuuid generation
Tweaks FromTime documentation to match conventions

Also adds me to AUTHORS
Merge pull request #86 from phopkins/custom-time-uuid

Fixes UUID Timestamp and add FromTime function