Add date timezone (z, Z, O, v, V, x, X) support

**Format**

 - [ ] Zone `z`
 - [ ] Zone `Z`
 - [ ] Zone `O`
 - [ ] Zone `v`
 - [ ] Zone `V`
 - [ ] Zone `X`
 - [ ] Zone `x`

**Parse**
 - [ ] Zone `z`
 - [ ] Zone `Z`
 - [ ] Zone `O`
 - [ ] Zone `v`
 - [ ] Zone `V`
 - [ ] Zone `X`
 - [ ] Zone `x`

Fix issues:
 - [ ] #186
 - [ ] #187 - possible default for format: {datetime: "long"}

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Docs:
- [UTS TR35: Unicode LDML Part 4: Dates](http://www.unicode.org/reports/tr35/tr35-dates.html#Supplemental_Time_Zone_Data)
- [CLDR Translation Guidelines: Time Zones](http://cldr.unicode.org/translation/timezones)