Fix documentation build
* Doxygen needs `RECURSIVE = YES` in order to parse the `detail` subdir.
* The `-W` warnings-as-errors option for sphinx doesn't work with the
makefile build. Switched to calling sphinx directly.
* Fix "citation [cppimport] is not referenced" warning.
diff --git a/docs/compiling.rst b/docs/compiling.rst
index 90b3829..67bd75c 100644
--- a/docs/compiling.rst
+++ b/docs/compiling.rst
@@ -14,10 +14,10 @@
Building with cppimport
========================
- cppimport is a small Python import hook that determines whether there is a C++
- source file whose name matches the requested module. If there is, the file is
- compiled as a Python extension using pybind11 and placed in the same folder as
- the C++ source file. Python is then able to find the module and load it.
+[cppimport]_ is a small Python import hook that determines whether there is a C++
+source file whose name matches the requested module. If there is, the file is
+compiled as a Python extension using pybind11 and placed in the same folder as
+the C++ source file. Python is then able to find the module and load it.
.. [cppimport] https://github.com/tbenthompson/cppimport