Merge pull request #27 from avidas/master

Merge xlevus's changes for allowing mutliple api objects in the same thread
Merge pull request #28 from avidas/update_requirements

Update requirements.txt to current
Merge pull request #29 from avidas/unicode_support

Unicode support added, Fixes #17
Merge pull request #30 from avidas/isolate_unittests

Isolate unittests
Improved `merge_dict` and included few docstrings

Python dictionaries have `update` method. That would be far more efficient than converting the `dict.items` to list and creating a `dict` at the end.
Cleaned up few lines of code
Cleaned up few lines of code

I am not very comfortable with the usage of `six`, which is not a built in module.
passing client id and secret always
Merge pull request #31 from thefourtheye/patch-1

Improved util.merge_dict and included few docstrings
Merge pull request #32 from thefourtheye/patch-2

Changes looks good now. Merging.
Merge branch 'master' of github.com:paypal/rest-api-sdk-python

Sync up with org master