Test edit: add to description of elevator
fix typo in (unused) implementation of define_action
added .gitignore file to make git ignore various temporary files that aren't part of the source
changed Location.first_time from a class variable to an instance variable: rather than a global variable tracking whether any room has ever been visited, we want each room to track whether it's been visited separately.

replaced all class variables (which I believe weren't meant to be class variables) with comments documenting the corresponding instance variables.

fixed typo so that first_time gets set to False rather than True after a room is described.
Improved behavior of proper_list_from_dict():
- added logic that adds appropriate article (a/an) to a noun
  based on whether it starts with a vowel
- add articles to all words in list, not just last
- omit comma if there are only 2 items in list
  (e.g. 'an apple and a pear')