Add Linux auto-installer for g++ with package manager detection

Author: pepc84

CppMode.txt

@@ -5,6 +5,6 @@ url=https://github.com/processing-cpp/processing.cpp
 sentence=Write and run Processing sketches in C++.
 paragraph=C++ Mode lets you write sketches using the familiar Processing API — size(), ellipse(), mouseX, draw() — but compiled to a native binary via g++. Runs on Linux and Windows (via MSYS2). Requires g++ and OpenGL (GLFW + GLEW).
 version=2
-prettyVersion=0.1.1
+prettyVersion=0.1.2
 minRevision=1293
 maxRevision=0