add progressbars, debug statements, and a MUCH faster parser for sparse
data sets
remove progressbars for fast items
use > instead of != since that was the original comparison
add an alternative implementation; it seems slower but is worth
discussion because I *think* there's a way to use this approach for
another few-times speed boost
remove commented alternative implementation.  Also, trigger travis build
implement 3 methods, with an option, and with performance tests [NOTE:
this is not mean to be merged but to exist in the git history as a
record of why a method was selected]
final performance stats: method 2 is slowest
'final' ish version: try scipy, fall back on slower but not terribly
slow version
split the slow/fast readers into functions
fix some bugs introduced in the functionalization
remove unnecessary in-place-ness and some other extraneous code
Merge pull request #131 from keflavich/faster_dendro_parser

Faster dendro parser
use travis
Merge pull request #135 from ChrisBeaumont/travis

Use travis
Adding wcs as an input initializing argument.
Renamed ax1->ax_image, added WCSaxes support when dendrogram.wcs is defined.
Renamed ax2->ax_dendrogram.

ax1 and ax2 seemed unclear to me so this should help the code naming scheme be clearer going forward.
Updated docstring for `wcs` kwarg.

WCS is used for the viewer.
Added wcsaxes to Travis requirements. (I hope this works.)
Added screenshot and snippet about WCS integration into the docs.