Call doxygen from cmake

Among other things, this allows to substitude project version into
Doxyfile

CMakeLists.txt

@@ -36,6 +36,8 @@ ELSE(SDL2PP_WITH_IMAGE)
 	MESSAGE(STATUS "SDL2_image support disabled")
 ENDIF(SDL2PP_WITH_IMAGE)
 
+FIND_PACKAGE(Doxygen)
+
 # compiler flags & definitions
 IF(MSVC)
 	SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W3")
@@ -75,6 +77,16 @@ CONFIGURE_FILE(
 
 INCLUDE_DIRECTORIES(BEFORE ${PROJECT_BINARY_DIR})
 
+# doxygen
+IF(DOXYGEN_FOUND)
+	CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/Doxyfile.in ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
+	ADD_CUSTOM_TARGET(doxygen
+		${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
+		WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+		COMMENT "Generating API documentation with Doxygen" VERBATIM
+	)
+ENDIF(DOXYGEN_FOUND)
+
 # sources
 SET(LIBRARY_SOURCES
 	SDL2pp/AudioDevice.cc

Doxyfile.in

@@ -38,7 +38,7 @@ PROJECT_NAME           = "libSDL2pp"
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 0.6.0
+PROJECT_NUMBER         = @SDL2PP_VERSION@
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a
@@ -753,7 +753,7 @@ WARN_LOGFILE           =
 # spaces.
 # Note: If this tag is empty the current directory is searched.
 
-INPUT                  = SDL2pp
+INPUT                  = @CMAKE_CURRENT_SOURCE_DIR@/SDL2pp
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses
@@ -788,7 +788,7 @@ RECURSIVE              = YES
 # Note that relative paths are relative to the directory from which doxygen is
 # run.
 
-EXCLUDE                = SDL2pp/external
+EXCLUDE                = @CMAKE_CURRENT_SOURCE_DIR@/SDL2pp/external
 
 # The EXCLUDE_SYMLINKS tag can be used to select whether or not files or
 # directories that are symbolic links (a Unix file system feature) are excluded
@@ -821,7 +821,7 @@ EXCLUDE_SYMBOLS        =
 # that contain example code fragments that are included (see the \include
 # command).
 
-EXAMPLE_PATH           = demos
+EXAMPLE_PATH           = @CMAKE_CURRENT_SOURCE_DIR@/examples
 
 # If the value of the EXAMPLE_PATH tag contains directories, you can use the
 # EXAMPLE_PATTERNS tag to specify one or more wildcard pattern (like *.cpp and