Add special MustacheNotFoundException to differentiate between compiler related and filesystem/resource related templating issues.

This allows clients to get the name of the missing mustache file and therefore enables better error handling espacially in the case of a ui where a user should be informed about the missing mustache.
Let the MustacheParser also use the MustacheNotFoundException.

This will be thrown when a template file could not be resolved by the MustacheFactory even when this might never be the case because the default implementation already throws this exception.
Merge pull request #104 from sbuettner/master

Add special MustacheNotFoundException to differentiate between compiler ...