Firmware upgrade: version 1.21

[Vectrex32]

There's a new version of the Vectrex32 firmware available, version 1.21. If you already own Vectrex 1.10 or newer, you can download the firmware here. If you still have version 1.00, please read this.

This version adds several new features and fixes a few bugs:

- Add run-time error handling with ON ERROR CALL
- Add 2.5D sprites, which are 2D sprites that can be positioned in the 3D world.
- Add binary file I/O with FRead and FWrite. Add random access with FSeek and FTell.
- Add byte arrays to support binary files.
- Add bitwise operators &, |, ^, and ~ (AND, OR, Exclusive OR, and Complement).
  WARNING: if you were using ^ for exponentiation, you need to change your code!
- Add the pow() function for exponentiation.
- Allow == for testing equality, since you can't teach an old C programmer new tricks. :-)
- Add SpriteGetUserData and SpriteSetUserData to allow a program to associate
  arbitrary data with a sprite
- Handle dual-port RAM overflows more gracefully.
- When re-DIMming an array, free the old array before allocating the new one. This
  is more memory efficient.