This renames "internal" recipes to use the Python3/ prefix and clarifies
the names (RunTarget to Run, Mod to ModSetup, Shebang to FixShebang).

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

This changes the recipe name prefix from Build/Compile/HostPy3 to
HostPython3, and clarifies some of the names (RunHost to Run, Mod to
ModSetup).

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

This is largely done by suffixing "python" or "py" with "3".  The
README.md file is also copied here and we intend to maintain it
independently from its python2 counterpart.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>