Enemies die on hit, game over dialog, version 0.5!!

Needs some cleanup however, late night coding resulting in messy code.
Merge pull request #172 from dreamteam69/master

Enemies die on hit, game over dialog, version 0.5!!
Garbage collection (remove off-screen entities)
Merge pull request #174 from dreamteam69/master

Garbage collection (remove off-screen entities)
Stack tracing for debug 24982f867aa0ee56dd5845cd5b0c72ba8275a709
Merge pull request #175 from dreamteam69/master

Stack tracing for debug 24982f867aa0ee56dd5845cd5b0c72ba8275a709
Background class
Merge pull request #176 from ping19/master

Background class
Background setup
Merge pull request #177 from ping19/master

Background setup
Adding background to canvas
Merge pull request #178 from ping19/master

Adding background to canvas
Renaming background image
Merge pull request #179 from ping19/master

Renaming background image
Allowing background movement
Merge pull request #180 from ping19/master

Allowing background movement
Adding background movement
Merge pull request #181 from ping19/master

Adding background movement
Code cleanup
Merge pull request #182 from ping19/master

Code cleanup