Move Rectangle2DInt to own header
Add global timer utils

Global timers can be used to accumulate timings of the same context
in a thread-safe way.
Use iterators for DouglasPeucker
Allow empty ranges in DP
Make atan2_lookup inline since it is header-declared
Add wrapper function to DouglasPlucker for backwards-compability
Use numeric_limits
Fix include order in staticrtree
Reorder include and use correct datatypes
Merge pull request #1217 from TheMarex/sketch-upstream

Bring general sketch commits upstream