Coin additions

[NyakoFox]

This pull request adds a few features, which don't¹ affect gameplay. It does the following:

• Reimplements the coin display from the VVVVVV SS1 prototype
• Makes coins use their own ID array in save files, instead of sharing the trinket ID array
• Adds coin editor entities² to allow external tools to use coins, and to help the game figure out when it should render the coin display
• Unlimits the coin amount and stores it differently than other collectibles

[1] Technically, making coins use their own ID array no longer allows level makers to use iftrinkets(x) to check if you've gotten coins, however the interaction between coins and trinkets made this hard to use anyway... I don't think any levels did this. [2] This PR adds coin editor entities, however it does not add a new editor tool. I personally just don't feel like I'm the one who should make such a big decision like adding a new tool.

Legal Stuff:

By submitting this pull request, I confirm that...

• [x] My changes may be used in a future commercial release of VVVVVV
• [x] I will be credited in a CONTRIBUTORS file and the "GitHub Friends" section of the credits for all of said releases, but will NOT be compensated for these changes