Use git.mk

It's a lot nicer than manually maintaining .gitignore in general.

Closes: #235
Approved by: giuseppe

apidoc/.gitignore

@@ -1,2 +1,51 @@
-ostree*.1
-ostree*.5
+*.lo
+*.o
+.deps
+.libs
+/*.bak
+/*.gcda
+/*.gcno
+/*.orig
+/*.rej
+/*.tab.c
+/*~
+/.*.sw[nop]
+/.dirstamp
+/.gitignore
+/GPATH
+/GRTAGS
+/GSYMS
+/GTAGS
+/ID
+/Makefile
+/Makefile.in
+/TAGS
+/gtkdoc-check.test
+/html
+/html-build.stamp
+/html.stamp
+/ostree-decl-list.txt
+/ostree-decl.txt
+/ostree-undeclared.txt
+/ostree-undocumented.txt
+/ostree-unused.txt
+/ostree.args
+/ostree.hierarchy
+/ostree.interfaces
+/ostree.pdf
+/ostree.prerequisites
+/ostree.signals
+/ostree.types
+/pdf-build.stamp
+/pdf.stamp
+/scan-build.stamp
+/setup-build.stamp
+/sgml-build.stamp
+/sgml.stamp
+/so_locations
+/tags
+/tmpl
+/tmpl/*.bak
+/tmpl/ostree-unused.sgml
+/xml
+_libs