Iambic Keyer / Transmitter update

I have posted a simple update to the keyer / transmitter project on Github.  The change allows you to specify which sideband you wish to use for the transmitter offset.  You specify the frequency the receiver will use and how much you want to offset your transmit frequency.  The idea is to be able to hear your own transmitter in the receiver as a sidetone.  By default I use 600 Hz offset from the receiver frequency.  When I drop down below 30 metres, I typically use lower sideband (LSB) and offset 600 Hz below the receiver frequency and on 30 metres or above, I offset 600 Hz above.  This can now be changed by setting the sideband value to LSB or USB as appropriate.  Previously to achieve the same effect, you would have had to change the toneOffset value to +600 or -600 as appropriate.