Implemented exec command.
Unit and integration tests for exec.
Shorten overlong line, fix indent.
Fix typo in exec url.
Updated README with description of exec.
Use shlex for exec string cmd, added integration testcase.
Merge branch 'exec' of github.com:phensley/docker-py into phensley-exec

Conflicts:
	README.md
git push origin masterMerge branch 'phensley-exec'