3.0.0

Breaking changes

• Removed scaled_sum / MagnitudeField (and decode_scaled_sum). Summing
  magnitude registers is value-composition that belongs in the consumer — declare
  the registers as fields and combine them in a @property.
• Removed write-unlock coil support (the level_coil field option). A coil
  that must be released before a write is device-specific write sequencing; do it
  by overriding Component.write() in your subclass.

Other

• The stride / index mechanism for repeated sub-units (e.g. heating
  circuits) is now documented in the README and the Component docstring,
  including the interleaved-by-register-type case where a sub-unit's fields each
  carry their own stride.
• Require tmodbus[async-serial]>=0.3.1 (communication-lock fix).