Set security token via environment or config file

Support AWS_SECURITY_TOKEN environment variable and
aws_security_token in the config file.  Unit tests and doc change
included.  Ignored updating core/ as I assume core is abandoned in
favor of the separate botocore project.
Add support for arbitrary dict inputs to MWS calls
PEP8
Add unit tests for instantiating the DynamoDB Binary type.
Merge pull request #1963 from danielgtaylor/ddb-binary

Require a string value to instantiate Binary DynamoDB type. Fixes #1963, #1956.
Merge branch 'rn-issue-dupe-fix' into develop
Fixes #1965
Altered cert failure checks for regions.

This should make the integration tests happier.
Merge pull request #1930 from oxtopus/consistent-identity-comparison-none

Consistent use of identity comparison (`is`/`is not`) for None. Fixes #1930.
Add EC2 associate_address_object method

Fixes #1874, #1893.
Adding unit test for table scan on specific attrs
Fixed a quoting bug of special characters in S3.
Populate both next_token and nextToken. Fixes #1968.

This bug was introduced due to an issue with how boto handled the nextToken
field in responses, which meant that it was exposed with the incorrect
name. The fix caused existing code to break, so now both versions are made
available. New code should use next_token.
Added release notes for 2.22.1.
Bumped to v2.22.1!
Merge branch 'hotfix-2.22.1'
Merge branch 'hotfix-2.22.1' into develop
Make sure associate address failure returns false

Modifies EC2 connection to use common code for both associate_address and
associate_address_object. False is now properly returned for associate_address
again, keeping backward compatibility.
Merge remote-tracking branch 'stevearc/scan_attributes' into develop

Fixes #1945.

Conflicts:
	boto/dynamodb2/table.py
Merge pull request #1967 from danielgtaylor/ec2-address

Add EC2 associate_address_object method. Fixes #1874, #1893, #1967.
Added attributes support to ``get_item``.
Fixes #1643 & #1877
Added a missing docstring.

:sweat: