Backport the CMAKE related changesets from the main branch

[e20fecd1945f] Add check target for CMake (#388)
[e74b5db4f2c6] Put the output of chg-len.py in the version string (#389)
[7d166b8b8018] Safer call of ./scripts/chg-len.py on Windows (#389)
[659ba4805a48] Make CMAKE config more consistent with configure.ac (#390)
[63e4468c680e] Add 'Maintainer' CMAKE build type (#388, #390)
[a725503acfe9] Allow CPACK configuration on all platforms
[10242c611190] Create and install lemon.pc (#393)
[48e29534cf03] The deafult target doesn't build lp_test and mip_test (#388)
[0fbbdd578c06] Full path for DoxygenLayout.xml in Doxyfile.in (#395)
[481496e6d71f] SOURCE_BROWSER Doxygen switch is configurable from CMAKE (#395)
[09282720100b] update-external-tags CMAKE target (#395)

 AM_CXXFLAGS = $(WARNINGCXXFLAGS)

 AM_CPPFLAGS = -I$(top_srcdir) -I$(top_builddir)

 LDADD = $(top_builddir)/lemon/libemon.la

 EXTRA_DIST = \

 	CMakeLists.txt \

 	digraph.lgf

 noinst_PROGRAMS = \

 	arg_parser_demo \

 	graph_to_eps_demo \

 	lgf_demo

 arg_parser_demo_SOURCES = arg_parser_demo.cc

 graph_to_eps_demo_SOURCES = graph_to_eps_demo.cc

 lgf_demo_SOURCES = lgf_demo.cc