Add Asia/Kolkata timezone

[srinivasreddy]

Pytz does not have Asia/Calcutta, it has Asia/Kolkata ; Kept Asia/Calcutta for backward compatibility

[ecederstrand]

Thanks for the PR!

The PYTZ_TO_MS_TIMEZONE_MAP name was badly chosen. CLDR_TO_MS_TIMEZONE_MAP would be better. The dict will be regenerated from time to time from the CLDR database using the generate_map() function, so your addition could get lost in the next update. I think it's better to keep extensions like this separately. Something like this:

PYTZ_TO_MS_TIMEZONE_MAP = {...}

# Add some timezone names used by pytz but not found in the CLDR
PYTZ_TO_MS_TIMEZONE_MAP.update({
    'Asia/Kolkata': 'India Standard Time',
})

[srinivasreddy]

Done.

[ecederstrand]

Thanks for the contribution!