Microschc

Bug fix on Context __repr__ function reference to ruleset.

PacketDescriptors are now hashable and have the raw packet content as attribute.

This release includes the IPv6 Payload Length, UDP Length and UDP Checksum compute-* functions.

0.15.4 introduces the no-compression rule as well as 2 strategies for matching frames to rules : `best` and `first`.

- `best` strategy goes through all rules of a context and returns the one that shows the smaller residue
- `first` strategy returns the first rule matching a frame, regardless of the compression performance.

What's Changed
* [bugfix] variable length field match by quentinlampin in https://github.com/quentinlampin/microschc/pull/17


**Full Changelog**: https://github.com/quentinlampin/microschc/compare/0.15.2...0.15.3