Fix Python compatibility

Fix #16 (#17)

Support for Yandex's side states

• support Yandex's side states (thx @uburuntu #14)
• run actions on PR (thx @uburuntu #15)

Compatibility fixes and updates

Maintenance update

• use safe_kwargs for the root AliceObject - AliceRequest (closes #13)
• update attrs version to 20.3.0 and update converter kwarg (closes #7)
• get rid of all relative imports
• run tests for different python versions
• update how 'install requires' gets list of required packages - needed for new python versions

Safe kwargs for all AliceObjects

• store raw json in models

Closes #9

Freeze attrs version

There’s a backward-incompatible change in attrs 19.2.0 (2019-10-01): Removed deprecated Attribute attribute convert per scheduled removal on 2019/1.
https://www.attrs.org/en/stable/changelog.html

So now attrs version is ==18.1.0

Update response timeout

https://yandex.ru/blog/dialogs/bolshe-vremeni-na-otvet-time-out-3-sekundy

Add fields and safe_kwargs to interfaces

Closes #4

Add original_request field to AliceRequest

Add some hints about testing and deployment into README
minor fixes

NLU, safe kwargs

• Support NLU

• Add safe_kwargs to meta and request

safe_kwargs will help ignore new JSON entities (if there's new API) so it won't cause exceptions

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NL..what?

Add `flags` to meta (Station Support)

A minor update for Yandex Station support