Are you sure all of the library files have actually been copied to the B4R library folder?
I ask this because when I updated the rIRremote and rIRremoteESP8266 to v1.01 and v1.13 respectively, to provide IR support for Foxtel cable/satellite TV boxes in Australia as per this
post I found that although I thought I'd copied the updated library files, they hadn't actually copied because administrator rights was required.
I added your PRONTO method to my rIRremote.xml, updated its version number to 1.02 and as per the screenshot, the function SendPronto is available. I can't test beyond that because I don't have a PRONTO device.