Add support for inverted RX and TX, and pull-up for RX

[ellepdesk]

Hi,

I've built an alternate circuit to interface with the EMS bus using a minimum of components:

The only drawback is that the RX and TX are inverted, and RX relies on the internal pullup if the ESP.

I've made a branch to hard-code these changes for me, but it may be useful for other users as well.
InvertRxTx-pullupRx

I would like to expose these settings in the webui, but I have no idea where to start.

[proddy]

I'd be ok to merge this and use DEFINES to determine if Rx and Tx are invested - that you can add to the build process (default is off obviously).

[ellepdesk]

Cool, I'll rework it to use DEFINES and submit a pull-request