Initialized sphinx documentation with a few turorials + added hessian to gauss_kernel

docs/Makefile

@@ -12,6 +12,11 @@ BUILDDIR      = _build
 help:
 	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 
+html:
+	$(SPHINXBUILD) -b html "$(SOURCEDIR)" $(BUILDDIR)/html $(SPHINXOPTS)
+	@echo
+	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html."
+
 .PHONY: help Makefile
 
 # Catch-all target: route all unknown targets to Sphinx using the new