docs: move todolist to own document, don't link in release build

It is always build for html, but not linked if the devbuild tag isn't
set. This tag is set in the Makefile if the $(BUILD_MODE) variable
isn't "release".

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

docs/Makefile

@@ -1,11 +1,5 @@
 include ../defines.mk
 
-ifeq ($(BUILD_MODE), release)
-COMPILEDIR := ../target/release
-else
-COMPILEDIR := ../target/debug
-endif
-
 GENERATED_SYNOPSIS := 						\
 	proxmox-backup-client/synopsis.rst			\
 	proxmox-backup-client/catalog-shell-synopsis.rst 	\
@@ -26,6 +20,15 @@ SPHINXOPTS    =
 SPHINXBUILD   = sphinx-build
 BUILDDIR      = output
 
+ifeq ($(BUILD_MODE), release)
+COMPILEDIR := ../target/release
+SPHINXOPTS    += -t release
+else
+COMPILEDIR := ../target/debug
+SPHINXOPTS    += -t devbuild
+endif
+
+
 # Sphinx internal variables.
 ALLSPHINXOPTS   = -d $(BUILDDIR)/doctrees $(SPHINXOPTS) .