Sort coordinates based on filename

In order to ensure consistent output of CSS between runs when the source
images have not changed, adjust the 'cleaning' function to a) sort based
on filename, and b) use an array instead of an object when calling
json2css.
Updated tests to use strictEquals comparisons

Now that the output should be generated consistently with each set of
input files on every run, it is safe to convert the tests to use
strictEquals to compare the actual/expected outputs.
Attempting to move to `JSON.parse` for comparing JSON
Found fundamental change to JSON.parse not properly running
Updated CHANGELOG
Release 1.7.0