Add the matcher sample back to the repo

[kbirk]

Hey there, while updating my project to the latest yojimbo changes I noticed that the matcher code was removed.

Years ago when I began using yojimbo in my projects I found the code in the matcher example extremely valuable for implementing the connection token logic. I am certain it is valuable to others as well.

If you are open to re-adding it, or putting it in its own repo, I've fixed up the Dockerfile and updated the code a little bit. The changes include:

• Removed the cgo dependency requiring libsodium, the golang.org/x/crypto package now provides a native go implementation of the crypto_aead_xchacha20poly1305_ietf_encrypt function.
• Switch from the gorilla/mux router to chi. chi is a very lightweight http router that uses the go standard lib interfaces rather than custom ones.
• Minor code convention changes to fit more into the idiomatic style of go. go vet no longer complains about things.

Thanks again for all the work you've done on these libraries and your articles on network programming!

[gafferongames]

Thank you. I was planning on adding it back in an integrated example form, but I didn't have time over the holidays to finish that work. This will be a good stop gap -- thank you