Original PR: #44

• Rewrote push to take advantage of local variables and functions instead of including non-API values in its own table. I also made it so that push no longer needs to call itself for functions, so push:function() is now push.function().
• Simplified and extended push's setupScreen function, it no longer changes LOVE's window settings, but instead adapts to them.
  • New format is now: push.setupScreen(pushWidth, pushHeight, {upscale = ..., canvas = ...})
    • upscale (string): upscale push's resolution to the current window size
      • "normal": fit to the current window size, preserving aspect ratio
      • "pixel-perfect": pixel-perfect scaling using integer scaling (for values ≥1, otherwise uses normal scaling)
      • "stretched": stretch to the current window size
    • canvas (bool): use and upscale canvas set to push's resolution
  • Window width and height can still be overridden using push.resize(width, height).
  • This (technically) fixes Setting window width/height to 0 in push:setupScreen causes blank screen #40.
• push now floors screen offsets internally to avoid drawing the screen in bewteen pixels.
• push no longer creates a new table every frame when using the canvas setting, fixing memory usage steadily increases when using canvases #28 (and potentially Performance is terrible on Android if canvas flag = true #42?)
• Removed push:setBackgroundColor(), since it was essentially just an integrated alias for love.graphics.setBackgroundColor().
• Removed push:apply(), since it was pretty limited in functionality, only serving as an alias for push:start() and push:finish() (plus, API changes will require devs to change their code anyway).
• Removed legacy LOVE 0.10 support.
• Removed Mario assets from repo, because Nintendo (replaced with new LOVE-inspired pixel art).
• Updated the README to showcase the new API, among other changes.
• Updated low-res example.
• Updated mouse-input example.
• Updated main.lua, commented out unsupported examples for now.

An additional note: I think the canvas API is really cool, but it could use a little cleaning up and tweaks. Its code is mostly untouched in my rewrite, so it should work the same for now.

Also, I wanted to make the screenshot on the README a GIF like the original one, but I wasn't able to record one properly.

NOTE: Everything in this changelog is subject to change, I have made more changes and experimental features that have yet to be uploaded.