Add checksum value for Axe FX III

[martinpavlas]

SysEx templates have to support Fractal Audio checksum calculation. see http://wiki.fractalaudio.com/axefx2/index.php?title=MIDI_SysEx#MIDI_SysEx:_calculating_the_SysEx_Checksum

Hi, I'm working on some Axe FX III implementation and noticed that they use a checksum for most of their SysEx. The implentation is here: http://wiki.fractalaudio.com/axefx2/index.php?title=MIDI_SysEx#MIDI_SysEx:_calculating_the_SysEx_Checksum 21h ·

Would it be possible to put this on the backlog, to get implemented? Just trying a simple scene change, with SysEx data that looks like this:

[
"F0",
"00",
"01",
"74",
"10",
"29",
{
"type": "value",
"rules": [
{
"id": 1,
"pPos": 0,
"bPos": 0,
"size": 3
}
]
},
{
"type": "checksum",
"algorithm": "roland",
"start": 1,
"length": 7
},
"F7"
]

I think I have it right, but just need the right checksum.