Add CMake doc target

* Added doc/CMakeLists.txt with doxygen target
* Moved Doxyfile to doc/
* Updated Doxyfile (removed obsolete variables)

doc/CMakeLists.txt

@@ -0,0 +1,17 @@
+FIND_PACKAGE(Doxygen)
+
+if(DOXYGEN_FOUND)
+	set(INPUTDIRS 
+		"\"${CMAKE_CURRENT_SOURCE_DIR}../src/core\"
+		\"${CMAKE_CURRENT_SOURCE_DIR}../src/gui\"
+		\"${CMAKE_CURRENT_SOURCE_DIR}../src/tracks\"
+		\"${CMAKE_CURRENT_SOURCE_DIR}../include\"
+		\"${CMAKE_CURRENT_SOURCE_DIR}../plugins\"")
+	CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/Doxyfile.in ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
+
+	ADD_CUSTOM_TARGET(doc
+		COMMAND ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
+		WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
+		COMMENT "Generating API documentation with Doxygen"
+		SOURCES Doxyfile.in)
+endif(DOXYGEN_FOUND)