Add Update Methods for Push, Contact and Device

[Furkanzmc]

I was creating a Safari extension for Pushbullet using this library and I needed to update things and it didn't have the methods. I realise that this is a big pull request, I could have compartmentalise the requests but I forgot. :smile:

[alexschneider]

Hey, thanks for the PR, I really appreciate it. Giving a cursory glance through the code, I've noticed that there are quite a few potential bugs. I'd like to get a test suite set up this weekend, so I hope you don't mind if I postpone merging until then?

Thanks again.

[Furkanzmc]

Not problem at all. Can you point out the mistakes so I can learn from them? Thanks.

[alexschneider]

I meant mistakes in my own code, sorry. I didn't specify that.

[KoalaBear84]

And, did you manage to setup a test suite? :)