Check cell comment

[pshriwise]

This adds a check in the __get_cell_cards method to check a token. This block throwing an error due to an attempt at creating a cell card object from a line beginning with " c" (space before the comment delimiter at the beginning of the line).

(Sorry for all the whitespace changes. I can submit a separate PR that only removes trailing whitespace for clarity if that's helpful)

Also, there may be a better place to insert this check. If so, I'm happy to move it.

[pshriwise]

Ping again :)