add option for use system libqrencode instead of submodule

[sl1pkn07]

Hi

is possible use libqrencode from system package instead of use from submodule?

Arch provide package for libqrencode (qrencode), and when install QRCodeSource create conflicts between both because install the same libs, headers and executable

greetings

[jeremypoulter]

I can certainly look at in, the sub module is mainly to ease use in Windows as well as provide a known working version.