Create class ScrollingLevelScreen
Set up world just like in TestLevelScreen, for test purposes
Implement basic, jerky scrolling
Refactor method for setting camera position
Camera doesn't scroll unless it's within the bounds of a level

The camera should only scroll when its left edge is within the left
bound of the level (level0), and when its right edge is within the right
edge of the level (levelEnd). 

I tried other methods of representing the level's size, like levelCenter
+ levelWidth, and level0 + levelWidth, but this way seems to be the most
intuitive for use.
Rename ScrollingLevelScreen -> TestScrollingLevelScreen

in preparation of extracting an abstract class ScrollingLevelScreen
Extract super class ScrollingLevelScreen
Enable demo
Allow camera to move unbounded when level bounds aren't set
Merge branch 'develop' into camera_movement

Conflicts:
	core/src/com/sweatyreptile/losergame/Player.java
Delete old log
Fix jerky camera movement

The issue was that the player still has velocity even when it stops
'moving'. To fix this, check instead whether player velocity in either
direction is not zero.
Create hasVelocity()

Properly compares floats
Use hasVelocity() to update the camera
Merge pull request #19 from SweatyReptile/camera_movement

Horizontal camera movement