Updates to the grunt task `data:meta`:
1. Pick "zone1970.tab" as its input source if available, defaults to zone.tab. (until 'tzdata2014f', only zone.tab was available, but now it's the deprecated version)
2. Output JSON of this task now has two hashes: "countries" and "zones" to facilitate consumers to deal much better with showing timezone choices.
3. Updated contribution docs to add info about "data-meta" grunt task.
Rebuild metadata for all 2014 releases according to the new schema
Merge pull request #162 from moment/country-metadata

Updates to the data:meta grunt task