Assembly-time math

There should be an [Operand](https://github.com/simon987/Much-Assembly-Required/blob/master/Server/src/main/java/net/simon987/server/assembly/Operand.java) type that allows assembly-time math. Example:
```assembly
MY_CONST equ 0x12
OTHER_CONST equ MY_CONST + 2
DW MY_CONST * 2
mov A, MY_CONST / 4
JMP [OTHER_CONST * 4 + 5]
```