buildPipe() function, edited buildHill() function

buildHill now takes in the top left coordinates followed by bottom right
coordinates as parameters.

.gitignore updated to ignore all .class files
buildCannon() function

Additional comments in all of my functions.
function testing in creat improved, .gitignore improved
more build functions

buildCoin, buildCoins, buildBlockEmpty, buildBlockCoin, buildBlockPower,
buildBlocksEmpty, buildRock