SWIG experiments

Squash of the following commits (a full rebase was too hard :( )
* ef309cfdf N - SWIG: create pm3.c (5 months ago)  <Philippe Teuwen>
* 05ba6a73f N - swig pm3_device -> pm3 (5 months ago)  <Philippe Teuwen>
* d59630183 N - swig: move pm3.i (5 months ago)  <Philippe Teuwen>
* 6adcfad75 N - Fix historic make & cmake (5 months ago)  <Philippe Teuwen>
* bcbef2edf N - Fix typo with script_embedded (5 months ago)  <slurdge>
* 538ee4dab N - Better SWIG integration: autogen func & attributes (5 months ago)  <slurdge>
* 756b62466 N - SWIG: few helper scripts (5 months ago)  <Philippe Teuwen>
* 47ba4acd0 N - SWIG %extend (5 months ago)  <Philippe Teuwen>
* 21841cb9d N - simplify scripts (5 months ago)  <Philippe Teuwen>
* 78c4f7929 N - Revert "SWIG experiments: introduce context" (5 months ago)  <Philippe Teuwen>
* 1562b75fc N - SWIG experiments: introduce context (5 months ago)  <Philippe Teuwen>
* a503dfcd9 N - SWIG experiments (5 months ago)  <Philippe Teuwen>

client/experimental_lib/example_py/01link_lib.sh

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+#!/bin/bash
+
+ln -fs ../build/libpm3rrg_rdv4.so _pm3.so

client/experimental_lib/example_py/02run_test.sh

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+#!/bin/bash
+
+#/usr/local/lib/python3/dist-packages/_pm3.cpython-38.so
+#/usr/local/lib/python3/dist-packages/_pm3.abi3.so
+#/usr/local/lib/python3/dist-packages/pm3.py
+#/usr/lib/python3/dist-packages/_pm3.cpython-38.so
+#/usr/lib/python3/dist-packages/_pm3.abi3.so
+#/usr/lib/python3/dist-packages/pm3.py
+
+# need access to pm3.py
+PYTHONPATH=../../src ./test.py

client/experimental_lib/example_py/02run_test_interactive.sh

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+#!/bin/bash
+
+PYTHONPATH=../../src ipython3 -i ./test.py

client/experimental_lib/example_py/test.py

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+#!/usr/bin/env python3
+
+import pm3
+p=pm3.pm3("/dev/ttyACM0")
+p.console("hw status")
+print("Device:", p.name)