Add basic panning input to GLFW client
Merge branch 'master' into glfw-input
Formatting
Fix panning and tapping callbacks

- Panning was using velocity but we now use displacement
- Mouse-up callbacks at the end of panning movements weren't handled correctly
Enable zooming in GLFW via scrolling callback
Add double-tap support and comments
Merge branch 'master' into glfw-input
Minor cleanup and one minor fix

- Panning was ignoring the first frame of movement; this (very small) discrepancy is fixed
- Add and re-word comments
- Shed some whitespace
Merge pull request #33 from tangrams/glfw-input

Glfw input
Merge branch 'master' into cont-zoom