Add package comment.

Add package comment, fix typo in error message, update link to
godoc.org.
Add contributor Gary Burd

Signed-off-by: Daniel Farina <daniel@fdr.io>
Call user.Current() only when "user" is not set.

Editorialized somewhat by Daniel Farina.

Fixes issue 69
Add contributor Ewan Chou

Signed-off-by: Daniel Farina <daniel@fdr.io>