Updates to lib/board.js (see description)

- Style nits;
- Removes else clause from Serial.detect (either it has a port or it needs to find one)
- Revert self = this aliasing
- Explicit this to all callback call sites.

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>
Adds example program illustrating use of Board constructor's |port| option

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>