Use custom XML instead of CSV for saving and loading files

Currently, CSV is used for saving monsters to a file, as well as for loading the list of all monsters. XML would allow for better handling of missing stats for some monsters, make the code for parsing easier to read, and make it easier to define custom monsters to import.

This would also apply to Players, although they are not implemented as of writing this issue.

Currently existing data, such as the master list of monsters, would need to be converted to XML, perhaps could be done with a small python script.

Example:

Eigorp

Goblin

...