doc/manuals: integrate into this repository

Update .gitignore and make the manuals build without a toplevel
configure.ac file from autotools:

$ cd doc/manuals
$ make

Related: OS#3385
Change-Id: I5916bc7e656b508fc74917e79841ce7e1ee4981b
diff --git a/.gitignore b/.gitignore
index a85b41a..47e9f86 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,14 @@
 selftest/trial_test/
 example/resources.conf
 ttcn3/resources.conf
+
+# manuals
+doc/manuals/*.html
+doc/manuals/*.svg
+doc/manuals/*.pdf
+doc/manuals/*__*.png
+doc/manuals/*.check
+doc/manuals/generated/
+doc/manuals/osmomsc-usermanual.xml
+doc/manuals/common
+doc/manuals/build