cmake: add version module
lib: don't detach kernel driver by default

Since this feature also disconnects running instances
of librtlsdr that claimed the device, it is now disabled
by default and can only be enabled at compile time.

To enable it when building with cmake:
cmake . -DDETACH_KERNEL_DRIVER=ON

To enable it when building with automake:
./configure --enable-driver-detach

Signed-off-by: Steve Markgraf <steve@steve-m.de>
bump version to 0.5.0

Signed-off-by: Steve Markgraf <steve@steve-m.de>