* Allow arbitrarily complex polygons in geod_polygon_*.  In the case
  of self-intersecting polygons the area is accumulated
  "algebraically", e.g., the areas of the 2 loops in a figure-8
  polygon will partially cancel.
* Simplify code by using C99 functions remainder and remquo.
* More test coverage.

Fixes to associated files:

* src/pipeline.cpp invoke geod_init with f = es / (1 + sqrt(1 - es))
  instead of (the less accurate) f = 1 - sqrt(1 - es)
* src/apps/geod_set.cpp remove "#undef f" (a dangling relic?).