PeriodType changed to "smart enum" class from enum
PeriodType changed to "smart enum" class from enum

zaccharles/nodatime,BenJenkinson/nodatime,jskeet/nodatime,nodatime/nodatime,zaccharles/nodatime,zaccharles/nodatime,BenJenkinson/nodatime,malcolmr/nodatime,jskeet/nodatime,zaccharles/nodatime,malcolmr/nodatime,nodatime/nodatime,zaccharles/nodatime,zaccharles/nodatime,malcolmr/nodatime,malcolmr/nodatime