cups-browsed 2.0.1

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 "=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)