#1149: only allow '+Pn' or '-Pn' for offsets
fix expanded year digit problem
#1149: add test
Merge pull request #1150 from benfitzpatrick/date-time.year-bounds-better-error

Fix missing num expanded year digit setting error
Merge pull request #1151 from benfitzpatrick/1149.integer-relative-final-point

#1149: require 'P' notation for integer cycling intervals and offsets