Added NSExceptions to Grid Generators and

moved audio files to strings
finished test cases
Created the Instructions backbone

Adding button and new view controller, backed the storyboard changes
with the new classes.
Added text for instructions
Merge branch 'develop' into feature-finishInstructions
added sound to buttons

Including instruction / back, credits/back, back from start game.
Added line about what spam is for bounce & sort
copied over storyboard template for instructions

added text of instructions
finished looking up instructions to game
Changes addressing comments.
Merge pull request #63 from zsweedyk/feature-validInputTests

Feature - unit tests that check for valid input.
Addressed Paula's comments.
Merge pull request #68 from zsweedyk/feature-PID-instructions

Added PID Instructions + changed Spam Instructions
Addressing excessive spacing
Fixed the spaces around =
Added transparency to the level complete pop up.
Changed nil check to negative
Merge pull request #75 from zsweedyk/bugfix-validInputTest

Changed nil check to negative
Adjusted font on the storyboard.
Merge pull request #76 from zsweedyk/feature-level-end-aesthetics

Feature level end aesthetics