Fixes#110 on Github. As the issue describes, `**` is not
the right syntax.
We could write `**/*.pyc` instead, but according to
https://git-scm.com/docs/gitignore a pattern already
matches at any directory level if it doesn't contain `/`.
Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>
This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.
