[suggestion] Use .stringsdict to properly represent plurals in all languages

[reggian]

I think the usage of stringsdicts would bring DateTools to a new level by offering proper support for all languages without the need to hack the strings files with "__" rules.

Apple Documentation

Simple example of stringsdict for Slovenian:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>dt_seconds_ago</key>
	<dict>
		<key>NSStringLocalizedFormatKey</key>
		<string>%#@seconds@</string>
		<key>seconds</key>
		<dict>
			<key>NSStringFormatSpecTypeKey</key>
			<string>NSStringPluralRuleType</string>
			<key>NSStringFormatValueTypeKey</key>
			<string>d</string>
			<key>zero</key>
			<string>pravkar</string>
			<key>one</key>
			<string>sekundo nazaj</string>
			<key>two</key>
			<string>2 sekundi nazaj</string>
			<key>few</key>
			<string>%d sekunde nazaj</string>
			<key>other</key>
			<string>%d sekund nazaj</string>
		</dict>
	</dict>
</dict>
</plist>

The example usage (with forced SL locale):

let locale = Locale(identifier: "sl")
let format = NSLocalizedString("dt_seconds_ago", comment: "")
let string = String(format: format, locale: locale, 1)