Add a unit test suite

[bbecquet]

Should have done it a long time ago… Will be useful for non-regression and the myriad of edge cases.

Some things to test, not exhaustive:

• [ ] support of every form of polyline/polygon/multi-poly*
• [x] parsing of offset/repeat options
• [x] projection algorithm:
  • negative, 0, 1, and > 1 offsets
  • 0 repeat
  • 0-length polylines
  • horizontal and vertical segments
  • correct number of symbols projected
  • correct angle

[bbecquet]

Mostly done since https://github.com/bbecquet/Leaflet.PolylineDecorator/releases/tag/v1.4.0