TSX instruction; transfer stack pointer to X.
Debugger "run" renamed to "continue".

Better consistency with GDB.
Debugger loads symbols from ld65 2.13.3 debug file.
Instruction.Op8 and .Op16 exported (was op8, op16).
Debugger resolves absolute instruction operands to symbols.

Example:

CPU PC:0xF4ED AC:0x00 X:0xFF Y:0x00 SP:0xFF SR:n-_b-i--
Next: JMP absolute $F07B (Main)
$F4ED > step
CPU PC:0xF07B AC:0x00 X:0xFF Y:0x00 SP:0xFF SR:n-_b-i--
Next: JSR absolute $F4C8 (StackInit)
$F07B Main> step
CPU PC:0xF4C8 AC:0x00 X:0xFF Y:0x00 SP:0xFD SR:n-_b-i--
Next: LDA zeropage $FF
$F4C8 StackInit> quit
Debugger has 'next' command; steps over JSR.
cpu.ReadInstruction() panics for illegal opcode.