Add extended RC5 20bits

[nicoboyfr]

Hello,

Would be nice if the support of RC5 20bits (use by Marantz amplifier) could be added :

Bits | description
1 | Start bit, always set
1 | Start bit, always set
1 | Toggle bit
5 | System
6 | Command
6 | Extension

There is a 3555 microseconds space after the 8th bit, so the timing of the trame looks like :
b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15 b16 b17 b18 b19

Thanks.
Marantz 2015 NR_SR_AV IR Command Chart.xls

[crankyoldgit]

See https://github.com/crankyoldgit/IRremoteESP8266/wiki/Adding-support-for-a-new-IR-protocol and collect some raw data first.