emulators/cannonball: Updates to 0.31

Changes since g20191023:

Maintenance Release

This release focuses on upgrading the libraries and compilation tools CannonBall
uses, as I hadn't maintained the codebase in a number of years. Most of these
changes will be invisible to most users. Right now, I'm trying to get the house
in order as opposed to add lots of wild new features! :)

• [audio] Audio updates at the correct rate and resolves the longstanding issue with music and sound being very slightly 'off'
• [roms] ROMs are now read by CRC 32 value. Filenames no longer matter - so long as they are present they can be renamed to anything.
• [roms] Fixed expected Z80 rom file length
• [controls] Start Button behaviour less 'sticky' and buggy
• [controls] Analog axis for accelerate and brake can now be configured via the in-built menu system
• [menu] Reduced delay when scrolling through menu with analog controls
• [config] ROMs and save data can be relocated to separate locations
• [bug fix] Time Trial mode no longer crashes if used as the first mode played
• [timing] Code tries to use V-Sync for timing OR internal timing, as opposed to both at once
• [source] SDL 2 used by default. SDL 1 removed from codebase. This appears to have fixed compatibility bugs for some people
• [source] Added compatibility for upcoming SmartyPi hardware (Pi 4 based) to run on original arcade hardware
• [source] A general clean-up in many areas