New Class MouseData
Written some failing tests.

FAIL: MouseData: Have a property x
FAIL: MouseData: Clear sets x to zero
FAIL: MouseData: Make copy x
3 new test passing

PASS: MouseData: Have a property x
PASS: MouseData: Clear sets x to zero
PASS: MouseData: Make copy x
MouseData.y

PASS: MouseData: Have a property y
PASS: MouseData: Clear sets y to zero
PASS: MouseData: Make copy y
MouseData.buttons

PASS: MouseData: Have a property buttons that is an empty Set
PASS: MouseData: Clear sets buttons to empty set
PASS: MouseData: Make copy of buttons
MouseData.clicks

PASS: MouseData: Have a property clicks that is an empty Set
PASS: MouseData: Clear sets clicks to empty set
PASS: MouseData: Make ingores clicks
InputData.clear() now returns this.

PASS: InputData: Clear sets version to zero and returns this