ST: debug -> develop refactor

also note python version
no cython bounds checking for div and magnitude
keep axis in coord slicing if picking out one point and rm_len1_mims is False
fix streamline obound1 typeo
change seed interface and supercharge cython streamline and interpolation

note that this commit changes the array layout of seeds and lines, they
are now 3 x n arrays instead of n x 3
add test_seed.py
add as_coordinates to line, plane, and volume seeds
better vector field shape detection
better matplotlib version checking
faster plane seed generating
bump version to 0.44

features: streamline, interpolation, and seed generation speed improvements
bugfix: matplotlib version checking
Merge branch 'release/0.44' into develop