improve cache busting to work with file paths

[dylanvu]

right now, in createHashMapOfFiles we create a hash map keyed by file name and value of the hashed file name.

However, as we saw in #123 , this causes any directories that happen to have the same name as the key value to be replaced incorrectly.

This can be avoided if we key the output of the createHashMapOfFiles and value with the actual path.

Example:

"highlight.js" : "highlight.123214.js" is the current behavior.

"/js/highlight.js" : "/js/highlight.123214.js" should be the new behavior.

Make sure highlight.js corresponds/maps well to the css references also.