run astyle on all C files in the repository

Leaves parse tests and generated files unchanged, and provides a style
filter for these.

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

licenses: convert license tags to SPDX

autocorres: activate regression test for nested struct access (VER-321).

autocorres: translate accesses to nested structs correctly. See tests/proof-tests/nested_struct.thy.

This should (finally) close issue JIRA VER-321. Unfortunately it also breaks some other things,
such as heap_abs_syntax, which we'll need to examine later.