Documentation of the new beautiful Interfaces and Interface-methods required [DOC102]

[firebird-automations]

Submitted by: Peter Vandel (petervandel)

README.plugins.html states:
"plugin may be written using any language, supporting pure virtual interfaces (you will need to rewrite interfaces declarations for your language if they are missing);"

Rewriting an interface declaration requires that detailed information is available about all method names and their signatures.
In addition, a detailed description of the Interface dependencies is very welcome. For example, how to obtain one interface from another?