feat: migrate to typescript

[JohannesLamberts]

closes #29

[JohannesLamberts]

the untyped 'promise-deferred' leads to tsc errors, but otherwise look good so far.

[JohannesLamberts]

@gajus 'promise-deferred' is currently missing types. I removed the dependency as the same can be archived with little code, also reducing dependencies.

If you dislike the change I could re-insert the module and either add types inside this repo (they don't need to be exported, since the Deferred is not public) - or add the types to DefinitelyTyped as suggested in ljharb/promise-deferred#9.

I'm looking forward to your review 🙂

[JohannesLamberts]

ahhh, now nyc fails. Otherwise, the tests are green.
I'll try to look into that tomorrow.

[coveralls]

Pull Request Test Coverage Report for Build 130

• 17 of 17 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.8%) to 91.327%

---

Totals
Change from base Build 126:	0.8%
Covered Lines:	139
Relevant Lines:	148

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 132

• 21 of 21 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.8%) to 91.327%

---

Totals
Change from base Build 126:	0.8%
Covered Lines:	139
Relevant Lines:	148

---

💛 - Coveralls

[JohannesLamberts]

@gajus thanks for the quick feedback. I don't know if you prefer to resolve the discussions. I went ahead and resolved them after my commit.

I also noted that I accidentally removed the --source-maps option and forgot to remove @babel/plugin-transform-flow-strip-types. Both have been adressed with the two latest commits.

I compared the dist file before and after the migration to make sure everything is ok. The only real difference apart from .d.ts instead of .flow files is the change of promise-deferred.

[gajus]

Thank you

[gajus]

🎉 This PR is included in version 6.6.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀