code refactored to follow pep8
tweaks, docstring and tests for stormpath.Error
refactoring, docstring and tests for auth.Auth
move related utility methods directly into auth.Sauthc1signer
remove stormpath.util module as it's needed no more
Error can optionally take the http status code directly

This is needed in reporting HTTP errors that don't have the
StormPath API error response object.
add requests wrapper dealing with auth and response/error handling
add DataStore for abstracting away the resource CRUD methods

For now a thin wrapper, will become more important when we add
caching to it.
refactor Resource

Unfortunately, this touches basically every line of code here, so
we might as well get over with it:

Resource changes:

* use new data store for resource creation/modification/retrieval
* store properties in __dict__ so we get accessors/setters for free
* autoloads all the attributes from the dict (still need to
  specify the writable attrs and related resources manually, tho)

ResourceList changes:

* make the create method reusable (with proper property/param
  name/value conversion from python_underscores to camelCase)
* slice-based offset/limit specification
* index-based get-by-href or get-by-index-in-list instance getter
* reworked iteration
refactor resources based on the refactored base Resource

A lot of code deletion, for great justice!
silence spurious linter warnings
no need to autoload everything into resource

As the library user will rarely need to use the resource classes
directly.
refactored client based on the resource refactoring
add unit tests for Resource and ResourceList
support for converting dict to search parameters
easier imports
return groupmembership when adding account/group to group/account
python 3.3 and 2.7 compatibility when using 64encode
modified new tests so they can be run manually
modified old tests to support refactored api