Update readme

[UniquePanda]

This updates the README.md to reflect the current state of the library. What this changes:

• Adds a Who created Resumable.js? section
• Updates some code snippets/defaults
• Updates explanations of some properties/functions
• Removes some obsolete properties/functions and adds some missing ones
• Adds documentation of the ResumableChunk class

I also moved the Events section behind the documentation of ResumableFile and ResumableChunk. That's why there is a big chunk of removed and added lines. I think it makes sense to review the readme as a whole anyways. Maybe I missed something that we want to change.

I didn't document some of the properties and functions because of #23. Instead I added corresponding todos (// todo #23) in the code.

[steffentchr]

@UniquePanda Did this PR go against the wrong repo?

[UniquePanda]

@UniquePanda Did this PR go against the wrong repo?

Ah yes, sorry. Forgot to mention! I really try to avoid this, but GitHub is making this unnecessary hard (by not allowing you to set a base branch for PRs that is in the forked repo and not in the upstream). 😄

[steffentchr]

No problem, just wanted to confirm this 👍