Routine name: kjt_get_key_buffer

Action: Returns values for monitoring the keyboard buffer

Input Registers: None

Output Registers:

HL = Location of the keyboard buffer WRITE index variable (The actual keyboard buffer starts 32 bytes lower in memory)
A = The value of the keyboard READ index variable.

Notes: On return, if A = (HL) no key has been pressed (IE: the keyboard buffer is empty)