Add plural rules

[janishorsts]

Add plural rules from CDLR. Ignore ordinal and range rules but consider them for future use.

Generate Golang files from CDLR data.

Option 1

Plural(locale string, v number.Formatter) (string, error)

Option 2

type Printer struct {}

NewPrinter(locale language.Tag) *Printer

func (p *Printer) Plural(v number.Formatter) (string, error)

func (p *Printer) Ordinal(v number.Formatter) (string, error)