if there are any comments that aren't "attached" to a message,
print them at the top of the generated file. we need this for
the fancy auto-gen'd dependencies in the tool-wiregen tests.
the RFC's extract-format.py is switching to a new format.
this script can correctly parse them.
mostly moves logic over from generate-wire.py, uses a
Python formatting libarary called mako, which needs to be
installed prior to running this script.
you can add it to your system with
sudo apt-get install python3-mako
