Activate the Doxygen documentation

Makefile

@@ -476,7 +476,16 @@ parallel :
 ###########################################
 # Cleanup
 
+.PHONY: clean
 clean :
 	/bin/rm -f $(Objects_ALL)
 	/bin/rm -f $(LIBDIR)$(VERSION)
 	/bin/rm -f $(EXECS)
+
+
+###########################################
+# Documentation
+
+.PHONY: docs
+docs :
+	doxygen ABACUS_Doxyfile && make -C docs/latex

README.md

@@ -25,6 +25,9 @@ $ make
 ```
 This will produce all executables, together with a library `ABACUS_[vn]` where vn is of the form [digit][character].
 
+## Documentation
+Documentation for the ABACUS codebase is generated using Doxygen. To generate the documentation, invoke `make docs` (you will need to have Doxygen installed on your system). The configuration file is `ABACUS_Doxygen`.  The HTML version is anchored at `docs/html/index.html`. The PDF version is located at `docs/latex/refman.pdf`. 
+
 ## Warnings
 * The ODSLF part (for one-dimensional spinless fermions) is not functional: it is based on the old Young Tableaux ids, and must be upgraded to `State_Label`s.
 * The Richardson part is not implemented; what exists is old and long deprecated.

docs/.gitignore

@@ -0,0 +1,2 @@
+*
+!.gitignore