TL;DR changelog:
- Reduce memory usage.
- Fixed edgecases which created invalid geometries.
- Improved UI (print total time, refresh input layers, removed 'repair
intersection precision' option for easier usage)

v0.50: (04-01-2016)
- improvement: removed repair intersection precision. Now segment intersection
automatically computes the best value.
 This reduces the amount of memory required in 'repair intersections' when a bad
value was set (default is always bad
 for many projections, and it required too much memory => kernel kills
process).
- bugfix: repair intersection now repairs two consecutive collinear line
segments.
- bugfix: repair intersection wasn't fixing line segment intersection in some
cases (thanks VasiliosKalogirou)
- bugfix: segment intersection detection was not finding all intersecting
segment pairs (changed raytrace to ddm)
- bugfix: in preserve topology, almost identical points were not unified on the
final simplified geometry
- bugfix: fixed edgecases in expandcontract in which a polygon that went
"inside-out" was detected as a correct contract.
- bugfix: input layer list now refreshes after adding/deleting layers, not when
simplipy window is reopened.
- dev: first unittests (to make sure new features don't break anything)
- dev: add docstrings and change codestyle to be more pep8