KLC document generic (standardized) relay and switch contact numbering scheme

[poeschlr]

Numbering scheme to use at least for parts that do not define one: (Taken from european standard i learned at school)

Full explanation from https://de.wikipedia.org/wiki/Relais translated:

A1, A2: Coil
11, 12: normally closed contact
13, 14: normally open contact
11, 12, 14: a changeover contact (11 is the common circuit, 12 is NC and 14 NO)
15, 16, 18: a changeover contact with special function. For example a time delayed one. Here 15 is again the common contact and it requires always to be connected to supply. 16 is NC and 18 is NO.

Originally brought up in KiCad/kicad-symbols#1134