Add some examples

[tnull]

We should add some easy-to-run-and-modify examples in an examples folder.

Basic starting point could be the examples from the README, but we could also add https://github.com/tnull/ldk-node-liquidity-poc there, for example.

[devrandom]

it would be nice if one of the examples was reasonably full featured, so it could be used to evaluate the library in a more complete way.