Correct type mismatches in PromiseKit.m
Replace kCFNull with NULL

The `void *` parameter accepts `NULL`, so there is no reason to pass it
a CFNullRef that needs to be bridged.
Use a bridged NSNull instead of a kCFNull

Getting an error because kCFNull is declared as a const. Using a bridged
NSNull instance fullfills the same purpose, without a warning.
Merge pull request #12 from Abizern/minor-corrections

Minor corrections
--warning

I believe this cast is correct.
Set HTTPMethod

Whoops.
Always log errors

In the interest of preventing errors from being silently absorbed. Let’s see how this feels.

Inspired by NSExceptions always logging when they are created/thrown or whatever it is.
Set a User-Agent, like AFNetworking does
Add ChuzzleKit as a submodule and a bootstrap script