Add Type Definition for Support Typescript & Add async function

[ReiiYuki]

Nowadays most of developer develop JS in the form of Typescript and using async function instead of callback design pattern. (I am one of that developer too lol)

So I add the type definition to this library and also add the async function for gitPullOrClone using as gitPullOrClone.async to enhance the ability of gitPullOrClone.

I hope this pull request will be merged.

Thanks 😄