Add support for DTEND, data types, and zoneless local date and date-time values

[simonratner]

This change adds:

• Support for DTEND (no duration concept, just validate and round-trip it) (DTEND seems to be an invalid property #322)
• Support for VALUE=DATE | DATE-TIME data types on DTSTART, DTEND, and UNTIL attributes
• Proper parsing and handling of zoneless local time values (they are stored without a tz specifier, instead of assuming UTC, and are round-tripped without the trailing Z suffix, as per RFC)

Because of this last change to tzid handling, this is a breaking change, but it implements zoneless values much closer to the RFC.

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[andjiev]

@jakubroztocil Can this be merged?

[Nuranto]

I also need this. Tried to build it but I can't manage to do it. (I'm not familiar with yarn/ts)
Could you merge it, or can someone explain how to build this ? (I have errors like Can't resolve 'ts-loader' or Error: Can't resolve 'source-map-loader'...)

[simonratner]

can someone explain how to build this

This works for me after setting target: es6 in tsconfig.json:

yarn install
yarn test
yarn run build

Find the output in dist/ directory afterwards.

[ratheep]

@simonratner , @jakubroztocil Wondering why this isn't yet merged with master ?

[georgiosgiatsidis]

Is this PR about to be merged?

[gazben]

@jakubroztocil Can you merge this?

[KrisLau]

@davidgoli

[frozencap]

damn. 3 year old PR implementing multiple highly-awaited features, doesn't receive a single comment from the maintainers :\