Fix the "elevation" in "elevation ruler"!

Improve path cleaning algorithm to remove multiple straight-line points. Closes issue #40.
Refactor measurement of distances and move distances to better account for 3d distance. Closes issue #41.
Remove animation easing for intermediate segments while keeping easing-in for the first segment and easing-out for the last segment.
Add CONFIG settings to change the unicode symbol displayed when the ruler is over terrain (or tokens, if tokens count as difficult terrain). Thanks @Aedif for the Font Awesome code example!

• CONFIG.elevationruler.SPEED.terrainSymbol: You can use any text string here. Paste in a unicode symbol if you want a different symbol. For Font Awesome icons, use, e.g., "\uf0e7".
• CONFIG.elevationruler.SPEED.useFontAwesome: Set to true to interpet the terrainSymbol as FA unicode.
  Update geometry lib to v0.2.15.

Breaking changes

The added methods Ruler.measureDistance and Ruler.measureMoveDistance were refactored and now take different parameters.

Full Changelog: 0.8.3...0.8.4