Better parsing errors

[Jimmy Cushnie]

Parsing errors currently only tell you what kind of error happened. Sometimes they quote you the part of the file that caused the error. Every time a parsing error is thrown, the following information should be included:

• the full path of the file
• the line number on which the error occurred

Parsing errors should probably be their own kind of exception as well.

[Jimmy Cushnie]

Implemented in #38 :D