Problem: clang-format not run on CI

Solution: add clang-format to cmake, and add another travis-ci build type

builds/cmake/Modules/ClangFormat.cmake

@@ -0,0 +1,36 @@
+# additional target to perform clang-format run, requires clang-format
+
+# get all project files
+file(GLOB_RECURSE ALL_SOURCE_FILES RELATIVE ${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_SOURCE_DIR}/*.cpp ${CMAKE_SOURCE_DIR}/*.h ${CMAKE_SOURCE_DIR}/*.hpp )
+
+if("${CLANG_FORMAT}" STREQUAL "")
+  set(CLANG_FORMAT "clang-format")
+endif()
+
+add_custom_target(
+        clang-format
+        COMMAND ${CLANG_FORMAT} -style=file -i ${ALL_SOURCE_FILES}
+)
+
+function(JOIN VALUES GLUE OUTPUT)
+  string (REPLACE ";" "${GLUE}" _TMP_STR "${VALUES}")
+  set (${OUTPUT} "${_TMP_STR}" PARENT_SCOPE)
+endfunction()
+
+configure_file(builds/cmake/clang-format-check.sh.in clang-format-check.sh @ONLY)
+
+add_custom_target(
+        clang-format-check
+        COMMAND chmod +x clang-format-check.sh
+        COMMAND ./clang-format-check.sh
+        #COMMAND ${CLANG_FORMAT} -style=file -output-replacements-xml ${ALL_SOURCE_FILES} >clang-format-replacements.xml
+        #COMMAND grep \"<replacement \" clang-format-replacements.xml >/dev/null && exit 1
+        COMMENT "Checking correct formatting according to .clang-format file"
+)
+
+add_custom_target(
+        clang-format-diff
+        COMMAND ${CLANG_FORMAT} -style=file -i ${ALL_SOURCE_FILES}
+        COMMAND git diff ${ALL_SOURCE_FILES}
+        COMMENT "Formatting with clang-format and showing differences with latest commit"
+)