Update serialize.py

double time imported

import datetime imported but unused

and fix PEP8 style
Update auth.py

from botocore.utils import percent_encode : unused
fix PEP8 style
Update compat.py

import datetime : unused
from urllib.parse import urlencode : double importded
from urllib import urlencode : double imported
Merge branch 'release-0.68.0' into develop

* release-0.68.0:
  Bumping version to 0.68.0
Add register_first/register_last in hooks module

Makes it possible to register hooks that you want called
before/after other hooks.
Refactor check_for_200_error to use register_first

No function change, this refactoring uses the new
register_first() method to ensure that we will always
be called before the general retry handlers.
Fixed version of unittest2 for travis
Merge pull request #368 from kyleknap/hook-register

Revamped register_first()/ _last()
Fix up pep8 formatting issues

Remove unused var.
Merge branch 'dslackw-patch-2' into develop

* dslackw-patch-2:
  Fix up pep8 formatting issues
  Update serialize.py
Fixup more pep8 formatting issues
Merge branch 'dslackw-patch-3' into develop

* dslackw-patch-3:
  Fixup more pep8 formatting issues
  Update auth.py
Merge branch 'dslackw-patch-4' into develop

* dslackw-patch-4:
  Update compat.py
Don't use credential provider if credentials are given

If the aws_* params are provided in a create_client() call,
we still call session.get_credentials(), which is an unnecessary
call.  We should only invoke the credential lookup process if
explicit credentials are not provided in the call to
create_client().
Merge branch 'fix-cred-prov' into develop

* fix-cred-prov:
  Don't use credential provider if credentials are given
Update service models
Bumping version to 0.69.0
Merge branch 'release-0.69.0'

* release-0.69.0:
  Bumping version to 0.69.0
  Update service models
  Don't use credential provider if credentials are given
  Fixup more pep8 formatting issues
  Fix up pep8 formatting issues
  Fixed version of unittest2 for travis
  Refactor check_for_200_error to use register_first
  Add register_first/register_last in hooks module
  Update compat.py
  Update auth.py
  Update serialize.py