Feature request: flag for Matrix answer checkers to check entry by entry

[dlglin]

It would be nice to have a couple of options for a Matrix answer checker to compare to the student answer entry by entry:

1. A flag to show the student which entries are correct and which are not.
2. A flag to award partial credit based on the number of entries in the matrix that are correct (e.g. if three of four entries are correct award a score of 75%).