finish separating 3 main HTML files and Javascript

build instructions in README.
code to build csv and json with NC names and centers

helpful for labeling NC polygons, and for drawing lines to the centers of NCs
start of static analysis for index page
fix bug where layers from each school selection were stacked. layers are now removed.
commented mistakenly committed popup and made layer remove a little safer.
Merge pull request #26 from sleitner/master

fix issue #1
separate post-load javascript files
style the NCs
highlight neighborhood on mouseover
hover-over shows NC names
first stab at display schools on click
draw lines from NC center to school
line mouseover gives counts