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.
This enables locating the headers within the install-tree using the
dirs provided by `zeek-config --include_dir`.
To enable locating these headers within the build-tree, this change also
creates a 'build/src/include/zeek -> ..' symlink.
The main change is that reassembly code (e.g. for TCP) now uses
int64/uint64 (signedness is situational) data types in place of int
types in order to support delivering data to analyzers that pass 2GB
thresholds. There's also changes in logic that accompany the change in
data types, e.g. to fix TCP sequence space arithmetic inconsistencies.
Another significant change is in the Analyzer API: the *Packet and
*Undelivered methods now use a uint64 in place of an int for the
relative sequence space offset parameter.
