Closes issue #322 | Add option to check if headset is connected

[theaino]

This closes issue #322. It adds the command line flag --connected alias -t (standing for test)
to check if there is a headset connected.

It works by first checking if a headset is detected.
If it does, there are 2 cases:

• a headset is connected and turned on
• a wireless headset's usb is connected but it is turned off

These 2 cases are differentiated by first checking if the
model has the battery status capability.

If it doesn't, it is wired connected.

If it does, the battery status is checked. If an error is returned, the headset
is turned off.

For example, this option can be integrated in bash scripts using
if headsetcontrol -t ; then ; <do something> ; fi

[theaino]

There is also true being returned when a headset
is connected making it compatible with the
test command.

[Sapd]

Thank you! However I would remove the -t short option and keep it for other purposes (given --connected is just used for scripting). To do so you basically set it to NULL and handle it in case 0:

I can also update the code in your branch but will not get to do so before next week

[theaino]

That makes sense. I just implemented and pushed it.