v0.10.2 Added Jupytext support and `ndlv` script for debugging cells.

• Jupytext integration #120:
  • Many thanks for Marc Wouts for adding support in Jupytext and @HaveF for the help and starting the topic.
  • Handle special commands to be prefixed with //gonb: -- this allows special commands to be parseable Go code, and makes it easier for IDEs.
  • Ignore package tag -- as opposed to raising an error: also to make easy on IDEs that may require a package tag.
  • Added special variation: %exec <function_name> <args...> that creates a main function that calls <function_name>
    and sets the program arguments (flags) to the given values.
• Added ndlv wrapper script for starting gdlv on cell binary.
  • Many thanks for @HaveF for the help -- see #122
• Notebook testing: changed nbexec to use system's google-chrome if available (with sandbox), or let Rod download
  chromium, but then use with --no-sandbox (since there is no SUID on the binaries).
• Fixed tracking to simply ignore loops, but not interrupt traversal during tracking.