Timber! Refinements

[LewisN3142]

• FPS counter.
• Clearer UI (semi-transparent black boxes behind text).
• Lighter and thinner trees in background.
• Optimise code that does not need to be executed regularly (i.e. sstream) and re-write some sections using functions/classes (i.e. an array of clouds) so that they may be reused in a more efficient way.
• Change cloud movement to be more realistic (tie speed to height and perhaps scale them).
• Flip player sprite when on the left side of the tree as currently faces away from the tree (need to set the origin of the sprite to centre or add a translation for this).
• Create a partial background sprite (no sky) which the clouds can move behind to add parallax.
• Investigate whether eventPolling can be exploited as it does not check which key is released.
• Remove unused sf::Time object at line 84 (not sure why this was added as it is never used, perhaps to track how long the player took to die/time-out? Perhaps I could implement this feature?).