Fix decoding N/A values (on DT inverters)

Fix decoding N/A power/energy values (mostly on DT inverters) so they report as None and not 0.
Add SELF_USE operation mode to ETT inverters and make operation mode handling bit more fault tolerant.

Add support for Modbus/TCP communication

Major rewrite of the communication protocol.
Besides existing Goodwe's Modbus/RTU over UDP, standard Modbus/TCP is now supported too.
New port parameter is added to connect() method - 8899 is assuming UDP, 502 is for TCP.

Add Peak Shavig limit and SoC settings

Add Peak Shavig limit and SoC settings.
Improve Eco Modes handling on ETT (platform 745).
Improve platform detection.

Fix sensors decoding on large inverters

Some sensors are defined as unsigned and were improperly decoded as signed, thus providing wrong values on large inverters.

Add support for new Eco Mode types

New inverter models/firmwares use newer encoding of Eco Mode schedules which now besides days in the week also contain months of year.
Improve feature detection (eco mode type) by querying registers instead of checking firmware version.

Add support for 3rd gen MS (MSC) inverters.

Add support for 3rd gen MS (MSC) inverters.
Fix decoding 0x55 as not-set value of EcoMode1
Fix battery cell voltage scale.
Limit arm fw version feature check to ETU inverters.
Improve UTF-16 strings decoding.
Add PV4 values to ETT inverters.
Fix unit of current in MPPT sensors.

Redesign sensor definitions and loading (they are addressed now by real modbus register).
Remove obsolete GoodWeXSProcessor and related code.
Remove support for unknown 'xx' parameters.

Add support for 2nd battery on ETT inverters

Add support for 2nd battery on ETT inverters.
Add support for MPTT sensors on ETT inverters.
Add support for extended meter sensors on ETT inverters.

Add support for 3 MPPT ET inverters

Add support for 3 MPPT ET inverters.
Remove export limit max values.
Fix issue #51.

Fix broken get_grid_export_limit on ES

Fix broken get_grid_export_limit on ES inverters

Add support for ES Gen 2 inverters

Add support for ES Gen 2 inverters (fix firmware parsing).
Fix sensors() on DT inverters.