Add MapInfo and ProgramInfo

Allow accessing map and program metadata. This also removes the confusing MapABI and ProgramABI, which have been deprecated.

Users of MapABI and ProgramABI can migrate to the Type(), etc. getters on Map and Program directly.

Support LSM hook and add network namespace link

The library now understands lsm/ sections. There is a new link.NetNsLink which allows attaching sk_lookup and flow_dissector programs.

Some bugfixes in btf.

Deprecate MapABI and ProgramABI

This release deprecates MapABI and ProgramABI in favour of straight up getters on Map and Program.