Finish documentation of Javascript client

[plcp]

The documentation of several parts of the Javascript client is not finished – for example src/stream.js – and is a requirement for a proper, usable library. Note that the exposed, user-friendly API must also be highlighted by inline documentation that refers to the example given – only stating that the user should only care for lnn.open and lnn.stream.tcp is not giving proper recommendations for using lightnion.