Add type annotation (Continue from #800)

[isac322]

Pull Request Checklist

• [ ] 🧪 Added tests for changed code.
• [x] 🛠️ All tests pass when run locally (run tox or make test to find out!).
• [x] 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• [ ] 📚 Updated documentation for changed code.
• [ ] ⏩ Code is up-to-date with the master branch.

Description of Changes

Continued from #800 . I worked after #800, but when I finished it, I did not know how to merge it into #800, so I created a new PR. Please let me know if you know how or if you can merge in another way. @krisfremen

I added the type to all the code. As I added, there were some parts that I thought were a problem, but I will leave a comment.

[jadchaar]

Hi @isac322 thanks a ton for the contribution. @krisfremen has been very busy, so he has been behind on updating his deprecation PR. I talked with @systemcatch today, and we have decided that I can work on shipping the py27/35 deprecation in a separate PR from Kris's. This will allow us to separate the deprecation from the addition of type annotations. You seem to be very knowledgeable with type-checking in Python, and we'd appreciate it if you could give us a hand there. But I think we should prioritize merging in the deprecation by itself so you can start clean on the type annotations from the master branch. What do you think?

[jadchaar]

@isac322 I worked with @systemcatch today to get a fresh deprecation PR up: https://github.com/arrow-py/arrow/pull/877. One this is merged, would you be open to transferring your work on annotations to the master code?

[isac322]

Hi @jadchaar, ok that sounds great! I will close this PR and open with rebasing later!