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)

 SET(LEMON_INCLUDE_DIR "@CMAKE_INSTALL_PREFIX@/include" CACHE PATH "LEMON include directory")

 SET(LEMON_INCLUDE_DIRS "${LEMON_INCLUDE_DIR}")

 IF(UNIX)

   SET(LEMON_LIB_NAME "libemon.a")

 ELSEIF(WIN32)

   SET(LEMON_LIB_NAME "lemon.lib")

 ENDIF(UNIX)

 SET(LEMON_LIBRARY "@CMAKE_INSTALL_PREFIX@/lib/${LEMON_LIB_NAME}" CACHE FILEPATH "LEMON library")

 SET(LEMON_LIBRARIES "${LEMON_LIBRARY}")

 MARK_AS_ADVANCED(LEMON_LIBRARY LEMON_INCLUDE_DIR)