v0.2.1

Main added features and changes:

• TikZ backend by @srush in #71
• Traces by @danoneata in #72
• Envelopes by @srush in #76
• Arrows and connections by @srush in #90
• Tutorials and examples: e.g, Big Ben by @srush in #78
• Gallery of examples by @danoneata in #39
• Documentation by @sugatoray, @srush and @danoneata in #53, #64 and #104
• Use planar library for geometry by @srush in #85 and #86
• Major code refactoring by @srush and @danoneata in #92 and #93