Added typescript definitions and jsdocs

[Inrixia]

This was actually already done in this pull request: https://github.com/gagle/node-properties/pull/32 But it was never merged for some reason. I've checked and the types are all still up to date.

[hlovdal]

This would be extremely useful. @gagle are there any obstacles to merging this?

[KevinGhadyani-Okta]

Is it possible we could get this merged?

[KevinGhadyani-Okta]

After going through this again, it looks like you need to type the callback functions. I'd expect it to be (error: Error, ...) rather than any for that type.

[KevinGhadyani-Okta]

Also, there's a use case for parse taking a source and callback without options. Currently, the type doesn't allow for options to be optional.