v2.2.0

This release mainly brings some bugfixes and the support for numerical font weights.

• #181: add support for numerical font weights
• #188: fix rendering two SVGs with the same ids in the same PDF document
• #187: fix exception when parsing CSS with @import rules
• #186: fix rendering elements with empty or invalid clip-path attribute
• #185: fix gradients with zero or one stop
• #184: fix bounding boxes and attribute inheritance for <marker> elements