Switch back to Guzzle 3, for compatibility with PHP 5.3

Signed-off-by: Peter Legierski <peter@legierski.net>
Bump version to 3.0.1

Signed-off-by: Peter Legierski <peter@legierski.net>
Update changelog

Signed-off-by: Peter Legierski <peter@legierski.net>
Merge branch 'hotfix-guzzle'