I added the two files required for the power up thruster. I forgot to add them in the previous commit.
I merged the development branch with the master branch. I made a change to the way the firepower is displayed and I added case statements to the key release and key pressed handlers so user input is preserved and updated during the LEVEL_NEXT state.

Merge branch 'development'
I cleaned up some unused imports.
All of the changes that I added to development over the past few weeks are now ready to be merged with master.

Merge branch 'development'
I am now moving all of my development changes to master since they have been tested and seem to work without any known problems.

Merge branch 'development'