Add a simple sample application that uses this module

[bgok]

When Catamaran swaps integrates this module, it will serve as a good, though complex, illustration of how the library works. Additionally, the integration tests illustrate how to call the public functions.

It would still be helpful to future users of the module to have a simple sample application to illustrate how the module works.

A DAPP that accepts Bitcoin for a Stacks NFT would be a great way to simply illustrate how the module works.