Switched to using dtslint from just running tsc --noEmit for typescript tests

[cameron-martin]

What:
Changed the TypeScript tests to using dtslint.

Why:

• Most importantly it lets you use $ExpectError to assert that a certain statement does type error, which the previous type tests did not.
• It also tests against multiple TypeScript versions.

How:
By changing from running tsc --noEmit to running dtslint for running the TypeScript tests.

Checklist:

• Documentation
• Tests
• Code complete

I'm having trouble running the dtslint tests for the react-emotion package - some of the features used in the dts files require a new version of TypeScript but I keep getting an error (microsoft/dtslint#78) when trying to use new versions of TypeScript.

This PR is just to make sure you agree with this direction before I pursue it even more and to collaborate if anyone else is working on it.

A few related changes, some as a side-effect of moving to dtslint:

• Made some changes to the dts files to satisfy the default dtslint rules.
• Renamed typings directory to types because this seems to be more standard.
• Renamed emotion.d.ts, etc to index.d.ts because dtslint seems to require this.
• Stopped "build" running before "test:typescript" as this is not actually necessary.

[renatorib]

That's great!

I saw that you renamed some names, like typings => types, react-emotion.d.ts => index.d.ts, etc.
I think this is not a good idea since all other emotion packages follows this names/structure.

Or, if you think this names/structure is better or necessary for that approach, you could rename from all other emotion packages also to maintain a consistency.

Edit: Sorry, I just saw that you already changed the other packages too

[cameron-martin]

I think dtslint requires that the dts file is named index.d.ts (although I could be wrong about this, I'll check). But yeah I'll make sure everything is consistent.

[cameron-martin]

The new version of dtslint has fixed those errors I was getting. I'm just getting a couple of errors with typescript@next (https://travis-ci.org/emotion-js/emotion/builds/292255135#L681), then this'll be done.

It's because of strictFunctionTypes, which is being introduced in TypeScript 2.6, which has got something to do with variance.

Any ideas, besides just turning off this flag?

[cameron-martin]

The above problem is now fixed.