Rename air.executableLocation and add air.executablePath support

[DavisVaughan]

Closes #243

• Renamed air.executableLocation to air.executableStrategy and updated documentation
• Added "path" option to air.executableStrategy
• Added air.executablePath

Reworked resolveAirBinaryPath() to be a series of if/else statements so it is extremely clear what all of the fallback behavior combination is. I think this dramatically improves both readability and the logging. I used Rust style Options by adding helpers like airBinaryFromBundled() that return string | undefined, which I think made the main function easier to read

I tested out each of these behaviors locally and am happy with the logging and errors

[lionel-]

Thanks!