doc: add Doxygen build system

- add Doxygen build configuration file template and CMake list file.
- add option for building documentation.
- the content of documentation should be filled in future.

doc/CMakeLists.txt

@@ -0,0 +1,6 @@
+# Configure Doxygen config file
+configure_file(
+    ${CMAKE_CURRENT_LIST_DIR}/Doxyfile.in
+    ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
+    @ONLY
+)

doc/src/index.dox

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+/**
+
+\mainpage YYCCommonplace Library Manual
+
+This manual is organized into the following chapters and appendices:
+
+\subpage intro
+
+
+*/

doc/src/intro.dox

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+/**
+
+\page intro Introduction to YYCCommonplace
+
+work in progress
+
+\section work in progress
+
+work in progress
+
+*/