Implement lowering of rest of operators

This pull-request implements the lowering of all other operators.

The operators not implemented are thoses one for which I could not get their correspondant BPF asm code, as libpcap had not support for those operators due to different issues: pf support (requires OpenBSD or FreeBSD), ATM support or 802.11 support.

Other issues:

- 'protochain' is not implemented. The obtained BPF asm code is rather large, so I preferred to leave it out for the moment.
- Operators 'vlan', 'mpls' and 'pppoes' modify the code obtained by next operators in the same expression. This should be taken into account. In addition to that, these operators modify their offset inspected on successive calls. That's implemented but due to some reason, it seems that the each expansion function is being called two times and that makes that the code generated is not correct.
- Apart from lowering implementation there are other fixes related to parsing of operators or expressions.
- I closed down all the other pull-requests related to lowering implementation.