Bugfix: axis ordering, was correct before
Also return plot extent, improved docs
Add plotting for MLA parsing
Added show_shwfs_vecs() to plot SHWFS data
calc_zern_basis(): Add modestart param

Sometimes (usually) we don't want piston modes, use modestart to skip a
number of modes.
Rename **slopes** to more descriptive **slopesi**

**slopesi** should be inverted matrix, not a slope matrix.
Renamed variable to non-keyword
Minor fix in docs
Improve documentation
Add features, bugfix to calc_slope

- Added zerncntr keyword as middle for Zernike polynomials (i.e. an
  offset between sub aperture pattern and Zernike polynomials)
- Added singval keyword to use a variable amount of singular values when
  inverting the zernike to slope matrix
- Re-use plot functions
- Fix issue with slopes matrix
- Added info when sub apertures fall outside Zernike polynomials
Don't list subaps, too many
Created 'examples', added opencv example

examples/ can hold code to demonstrate stuff. The first example is
opencv.py showing how to query a camera image and manipulate it. After
toying around this can (should) be incorporated into a auto-testing
module.
Fix crop windows for 0 shit in crosscorr

If crosscorr is given 0 shift for one dimension, it should calculate
xcorr only in the other dimension. This is fixed now.