year-quarter time format

[akariv]

Add a new datatype for denoting yearly quarters (which apparently is quite a common thing).

Proposed name: yearquarter (following the existing yearmonth)

Formatting:

• default format yyyy-Qq, e.g.: 2015-Q1, 2013-Q4
• format parameter: Same as in date, with these extensions: - %q should be used to indicate a numeric quarter number (between 1 and 4) - %Q should be used to indicate a quarter number in Roman numerals (case insensitive, between I and IV)

cc: @zelima

[Stephen-Gates]

Should be clear in spec that Q1 = 1 Jan to 31 Mar, etc.

[rufuspollock]

I thought about this when I introduced yearmonth and year #105 - how often do quarters show up and do they need their own type? This is a classic "feature" vs "complexity" trade-off and i'd like more data before we made a decision.

Re @Stephen-Gates we should at least be clear how people can translate / interpret this stuff now.