fix lexical sorting bug when calculating next todoid
get rid of variable which is only used once
use a filtering function instead of where()

This fixes filtering for todos which don't yet have a 'checked' attribute.
rename the order attribute to id

this way Backbone knows it should PUT on saving instead of creating
another record with POST
toggle checked state and save to the database
add style for striking through checked tasks
implement mark all as complete
fix XSS vulnerability by escaping task text
don't input empty tasks
cosmetic fixes: whitespace, a typo and a comment
add README