added string formatting to PersianDateTime
added one letter format infrastructure and "g" format to PersianDateTime
Merge branch 'persianDateTimeFormat'

Conflicts:
	src/FarsiToolbox/DateAndTime/PersianDateTime.cs
	src/FarsiToolbox/DateAndTime/PersianDateTimeFormatInfo.cs
	src/FarsiToolbox/DateAndTime/PersianDateTimeFormatter.cs
	src/FarsiToolboxTests/PersianDateTimeTests.cs