Xenomai runtime: report and mitigate when PLC cycle overruns.

Side effect :
_Log* macro was changed in plc_Xenomai_main.c,
and fixed in plc_Linux_main.c

SVGHMI: Do not generate Popen call when comamn is empty.

Fix python path in readme.

Python runtime: ensure that python thread finished before returning from StopPLC.

C runtime: initial fixes. Now runs and traces first_steps example.

beremiz_runtime -v -t tcp -p 61131 -h localhost

IDE: fix eRPC exception handling

All Runtimes: Now sizeof(tick)=4 on all platforms (unsigned int).

eRPC: update erpc version, add readme

C++ runtime: WIP. Continue PLCObject implementation.

Tests: fix wx_widgets.pytest/test_CustomIntCtrl.py

Merge commit 'e2df70b60b84031d3ccd3ae799a4e3aa8112f3ff' into python3

Doc: Add about section (PR #33)

* added about section

* updated .gitignore to exclude doc/_build/

ERPC: fix SetTraceVariablesList interface

This fix debug not suspending when having no variables, and other debug error being not reported.

C++ runtime: WIP: untested PLCObject implementation. Still missing tracing.

Update revisions used in tests running on GitHub.

merge

C++ runtime: add eRPC server, minimal CLI and Makefile. WIP.

More documentation. Work in progress.

IDE: Fix crashing non-thread safe code using Zeroconf

BACnet: Fixed grid cell choice editor. Consequence of wxPython4.

SVGHMI: fix font embedding with py3

IDE: Fix Variable grid ignoring edits. WxPython4 consequence.

IDE: Remove all occurrences of deprecated wx.grid.PyGrid

Merge commit '80e123b34e488ffea851dc2168b366ba6124c09b' into python3

Doc: start converting Standard Library documentation from old MC8 manual.

merge

Modbus: fix test: add missing filles and add Modbus source+build in GH CI

Modbus: add CI test + test project

Doc: re-organize existing, sketch outline, add SVGHMI intro.

Examples: add svghmi_json_table

SVGHMI: add "DISCARD:" prefix to force discarding an SVG element

SVG: fix HMI:Assign widget to properly handle single-letter variable names.