Migrate extent.py to extent.pyx
  - Replace some tuples (ul, lr) with C arrays.
  - Replace some tuple operations with loops.
  - Merge slicing.pyx to extent.pyx
Migrate extent.py to extent.pyx
  - Replace some tuples (ul, lr) with C arrays.
  - Replace some tuple operations with loops.
  - Merge slicing.pyx to extent.pyx
Compatible with old cython
Try to fix Travis CI unittest error
Again, this commit is to be compatible with older Cython. Local unittest pass.
Better naming, coding style for extent.pyx.
Remove old version code.
Merge pull request #37 from fegin/master

Migrate extent.py to extent.pyx