This largely copies over Spicy's `.clang-format` configuration file. The
one place where we deviate is header include order since Zeek depends on
headers being included in a certain order.
maintenance fixes for variadic run-time checks, '_' placeholder identifier
"-O allow-cond" permits compiling scripts to C++ when influenced by @if conditionals
more robust standalone compile-to-C++ properties
fix for nested "when" statements
test suite updates
