Allow to divide a register value by a number

[virtualdj]

Add support for a new parameter scale_division in the YAML definition files which allows to divide the register(s) value by a constant number provided. The division is always done after the scaling happened.

This is useful for example for registers that display a value in minutes, but you want the sensor to be in hours: in that case, simply add scale_division: 60 and change the unit of measurement accordingly.

So this sensor:

- name: "Total Generation Time"
  class: ""
  state_class: "measurement"
  uom: "min"
  rule: 3
  registers: [0x0428,0x0427]
  icon: 'mdi:clock-outline'

can be transformed to this:

- name: "Total Generation Time"
  class: ""
  state_class: "measurement"
  uom: "h"
  scale_division: 60
  rule: 3
  registers: [0x0428,0x0427]
  icon: 'mdi:clock-outline'

If you want days from minutes, supply scale_division: 1440 (60 * 24) and so on...
I took the opportunity to fix a bunch of typos in the customization readme, too.