Small type in test database name

NOTE:
':memory;' should be ':memory:', I remove NAME as django will be
automatically use in-memory if there is no NAME specified.

[ci skip]
Code formart according to flake8

1. format code
[ci skip]

Conflicts:
	recommends/listeners.py
	recommends/tasks.py
	recommends/tests/tests.py
reomoved deprecaded import
travis settings update

1. Change pip install order, should install django at last
2. Add flake8 to check code style
Clean settings.py format

accroding to flake8
Add documentation and small CI change

1. update AUTHORS
2. update documentation
3. change CI settings to show django version

Conflicts:
	recommends/storages/base.py
PEP 8
updated setup.py
skip tests for pyflake8
Change requirements.txt

move flake8 to test-requirements.txt
add dateutil in requirements.txt

[ci skip]
Add use_raw_id option for similarities and recommendations

1. Add use_raw_id option (default = False) to all storages
2. Add test for returned raw id list

[ci skip]
Add content_type_id as suggested

1. update documentation to have list example
2. return content_type_id in the list, now is list of dictionary
3. autopep8 all python code
4. change travis settings

Conflicts:
	.travis.yml
	recommends/storages/base.py
	setup.py
Fix flake8 error

1. The E126 never shown in my local env as I didn't upgrade pep8 which
is now 1.4.6