feature request: wave_add_serial inverting, enabling

[eslavko]

Hello... Pigpio has bitbang receiver for serial data with ability to invert signal. On the other side for transmitting with "wave_add_serial" there are no inverting possible. So wave_add_serial with inverting posibility should be nice. The other thing is "enable signal" in some cases. For example using RS485 transciver has separate enable signal to enable transmitter. Using pigpio.write to control enable signal is bad as large timing gap is issued. There is option to use wave chain but this give other problems.