Added error checking with diagnostic messages.
Connected property is working now as inteded.
Added device index property for motors and sensors.
S4 classes now use constructors as initializers.
Added cached value for dp_scale and num_values
Added checks for index out of num_values in Value and ValueFloat functions
Changed function speak to Speak in all files
Fixed some typos
Added missing constructor for leds and power supply (after rewriting as initializers)
Added prerequisity note for remote scripts:
-installation of ssh on PC (for automatic uploading of scripts and creating directories)

Added ignore.stderr to Speak command (so that it can be evoked remotely without problem, "Playing wav..." is normally output to stderr)
Just keep in sync

Merge remote-tracking branch 'upstream/develop' into develop
Merge pull request #17 from bmegli/develop

Tidy up R binding