Add updateIn, getIn, setIn, removeIn

[benbrimeyer]

I'm back from #4.

Adds the following methods to Dictionary:

• updateIn(dictionary, keyPath, updater, notSetValue)
• getIn(dictionary, keyPath, default)
• setIn(dictionary, keyPath, newValue)
• removeIn(dictionary, keyPath)

Implementations and test cases are similar to Immutable.js's implementations of these methods.

Todo:

• [x] Implementation
• [x] Write tests
• [ ] Make sure this is something we would want to add
• [ ] Documentation

[benbrimeyer]

@freddylist Should I proceed with this PR? I'd like to get the greenlight that this is something worth contributing.

[freddylist]

Hello, thanks for the PR!

Any new features to Llama are probably not worth pursuing at the moment; I have just updated the readme with a notice that I will no longer be maintaining Llama.

If it's ok with you, I will just leave this PR hanging. :)

Thanks again!