OpenPrinting cups-browsed Files

Bug fix release: Collected fixes of one year, mainly reliability issues. - Ignore attributes with IPP_TAG_NOVALUE We don't need to record attributes with IPP_TAG_NOVALUE value tag, cupsd will decide what to use based on the incoming document (Pull request [#33]). - Ignore attributes with empty values Previously, if IPP attribute value was empty, cups-browsed saved the attribute as printer option "<name>=0", e.g. orientation-requested=0. Often 0 is invalid and as no cluster member printer has this value therefore a job with this value gets rejected (Pull request [#32]). - README.md: Use MarkDown for link to bug tracker (Pull request [#31]) - Initialize variables to not get used uninitialized (Pull request [#26]) - Fix memory leak found by valgrind (Pull request [#26]) - Fix the daemon crash when get-printer-attributes fails cups-browsed crashed when it found a remote CUPS queue shared by mDNS on local network, but IPP request for this queue failed. The empty prattrs data structure is later accessed, which causes the crash (Pull request [#25]). - Better handle damage of queues created by cups-browsed cups-browsed-generated print queues are marked with a cups-browsed=true attribute. Sometimes it gets lost and the queue not considered cups-browsed-generated any more. As queues with implicitclass://... device URI are always from cups-browsed, ignore the missing flag and always restore them as cups-browsed queues, so that cups-browsed assigns a destination printer for each job (Issue [#429]) - Fix build with Avahi disabled (Issue [#19], Pull request [#20])