build-sys: move gtk-doc stuff into its own subdir and reindent autogen.sh

We moved most other build noise files into their own subdirs, so let's
do this for gtk-doc too

docs/gudev/.gitignore

@@ -1,3 +1,4 @@
+/*.bak
 /gtk-doc.make
 /version.xml
 /Makefile
@@ -12,6 +13,7 @@
 /gudev.interfaces
 /gudev.prerequisites
 /gudev.signals
-/html/*
-/xml/*
+/html/
+/xml/
 /*.stamp
+/tmpl/

docs/libudev/.gitignore

@@ -12,6 +12,8 @@
 /libudev.interfaces
 /libudev.prerequisites
 /libudev.signals
-/html/*
-/xml/*
+/html/
+/xml/
 /*.stamp
+/*.bak
+/tmpl/