Added comment for `command` argument

Added comment for the variable type of `create_container`'s `command` argument
Added validation for volumes parameter - Issue #276
PEP8 compliance - space between numbers and operators
Validation for volumes parameters as string in _container_config
Remove unicode type in isinstance
Create test for volume as string
Stop timeout should be added to the request timeout

Using the max of the stop timeout and request timeout did not entirely
make sure that a stop timeout greater than a request timeout wouldn't
fail prematurely with a HTTPTimeout exception. The correct behavior is
to add the timeouts together, as the stop timeout is understood to be
part of the "request processing time". Any transport-level timeout thus
comes in addition to that.

Signed-off-by: Maxime Petazzoni <max@signalfuse.com>
Merge pull request #292 from mpetazzoni/stop-timeout

Stop timeout should be added to the request timeout
Change str type for six.string_types to py3 compatibility
Merge pull request #291 from yograterol/master

Volumes parameter on create_container should be validated as string
Amended create_container documentation
Merge branch 'ifraixedes-patch-1'
Version back to x-dev
Allow pushing a single tag.
Closes #282
pep8 fix
Merge branch 'cameronmaske-push-tags'
first cut of restart policy
removed DeprecationWarning @shin-
added documentation for restart policy
Merge pull request #304 from shreyu86/dev-restart-policy

Restart Policy for Containers Implemented fixes #302