Removed bug in lensutil.sbmap

Distortion correction due to lensing needs to start with 2D x and y
matrices, not zeros.
Added a line in config.py that specifies the number of walkers to use.

I thought this could be another issue causing the bad fits, but it’s
not.
Finally pointed the DEET in the right direction.

g_image is the unlensed image of the source.  g_lensimage is the lensed
image of the source.  So, sample_vis.uvmodel was operating on the
unlensed source image, not the lensed source image.  No wonder it kept
failing to find a good fit!  This probably explains the difficulty I’ve
had modeling FLS3 as well.
Updated plot realizations.py

 Now accommodating hdf5 files and revised object name.
Documentation update

Now referencing "config.py" instead of "config.txt"
Merge branch 'pr/1'

Conflicts:
	sample_vis.py
	uvmcmcfit.py

This merge did not do what I wanted, which was to update master with
pr/1.  The problem: files in master were updated more recently than the
corresponding files in pr/1, so git assumed master was the correct one.
Revert "Fixed bug in lensutil.sbmap"

This reverts commit da4b83721dc7f8ac0d3d2aa41c84a1608f520a5f.
Revert "Rollback to python 2"

Finally figured out which commit needed to be reverted.

This reverts commit cdaa14ef6624b02bf1a3cb1e044c5777d54017cb, reversing
changes made to ac96b075d8919caa18dd818ab0ba1608cb888548.

Conflicts:
	sample_vis.py
	uvmcmcfit.py
Minor encapsulation and generalization.