Change TCP server socket data size indicator from Go/Protobuf specific to Bitcoin-style varints which are easy to implement in every language

[narodnik]

Also added Python example in extern/ ... able to move to another dir such as example/ if preferred

[codecov-io]

Codecov Report

Merging #64 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop      #64   +/-   ##
========================================
  Coverage    27.32%   27.32%           
========================================
  Files           16       16           
  Lines         1680     1680           
========================================
  Hits           459      459           
  Misses        1163     1163           
  Partials        58       58

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