Add support for multiple delimiters in PacketLengthParser, as well as delimiters of sizes > 1 byte

[bbeck13]

I've used this for a situation where the delimiter can be many different things each specific delimiter denotes a type of packet, and because there are so many it has to be multiple bytes. This doesn't break any existing functionality and consumers do not need to use this if they stick with the defaults.

I've updated the documentation for this here
serialport/website#125

[bbeck13]

#2679

So there's at least one other person who wants this.

[zellb]

Is there any chance this will get merged?

[bbeck13]

Is there any chance this will get merged?

I wish I'm not sure who to @ to move this along

I ended up building my branch into the projects I'm using this for feel free to do the same, kind of annoying bc it doesn't publish anywhere but not the end of the world

[bbeck13]

[reconbot]

This isn't my full time job or my family, I'm able to maintain serialport the best I can.

The feature however is great, glad to have it. I can't merge this as is because of the version bump and merge with master, however I can cherrypick your commit with the new feature in a new branch, your name will still be on the commit.