New option for reading out the setting of the bias-tee added.

[OrbitTheSun]

NEW OPTION

This branch implements an option for reading out the setting of the bias-tee.

With option '-g' the setting is displayed:

rtl_biast -g

Together with the '-b' option one can verify the setting immediately:

rtl_biast -b1 -g

Or in short:

rtl_biast -gb1

BUILD AND INSTALL

mkdir build
cd build
cmake ..
make
sudo make install
sudo ldconfig /usr/local/lib

[hayguen]

i have something quite similar in https://github.com/librtlsdr/librtlsdr/tree/development
as stated in https://github.com/librtlsdr/librtlsdr/blob/development/README_improvements.md :

functions were provided from Marko Cebokli at http://lea.hamradio.si/~s57uuu/mischam/rtlsdr/ports.html

but i never opened the case and tried reading the GPIO state.
could you test this? .. and eventually open an issue or pull request there?

by the way: what is your application for reading the state?