Added support for various compression formats for Packages download.
Added support for various compression formats for Packages download.

Now xz (apparently the new default), bzip2 and gz are supported.

Zspark23/raspbian-ua-netinst-1,matt2005/raspbian-ua-netinst,beylsp/rpi-installer,firepick/FireHawk,kolargol/raspbian-ua-netinst,beylsp/rpi-installer,malsony/raspbian-ua-netinst,daytonpid/FireHawk,FooDeas/raspberrypi-ua-netinst,Zspark23/raspbian-ua-netinst-1,racing-tech/rrp-raspi-installer,Zspark23/raspbian-ua-netinst,bbinet/raspbian-ua-netinst,cybercircuits/raspbian-ua-netinst,Zeerix/raspbian-ua-netinst,Zspark23/raspbian-ua-netinst-1,dicer/raspbian-ua-netinst,yodaaut/raspbian-ua-netinst,racing-tech/rrp-raspi-installer,krazedkrish/Web-Pro-ua-netinst,jturner314/raspbian-ua-netinst