Create exceptions file to house all of the convert specific exceptions.
Refactored 'exporter'
Lots of changes....
Removed uneccessary jinja_filters class.  Merged code into exporter class.
Additional refactoring in exporter class
Moved wrap code into Strings utility file.
Moved more code to Strings utilities file
Removed "profiles"...  Templates that are shipped with nbconvert by default should
have settings built into exporter.py class.  If the user wants to add a new template
and use profile setting with it, the "profile" (config file) should be specified
via the commandline when calling the exporter.