cups-filters 2.0.1

Bug fix release, mainly fixes on the build system, but also on the serial backend

• serial backend: Fixed bug in conversion of comments
  (Pull request #548)
• pclmtoraster: Properly set CFLAGS
  As this is a C program, set pclmtoraster_CFLAGS, not pclmtoraster_CXXFLAGS (Pull request #588).
• configure: Remove == bashism
  (Pull request #567)
• configure.ac: Remove Avahi check
  cups-filters does not use Avahi (Pull request #558)