create a sub-dir for moon's doc

Change-Id: I06b66843f4bef550c6312a5f668f47d6861d6369
Signed-off-by: WuKong <rebirthmonkey@gmail.com>

diff --git a/keystone-moon/doc/source/extensions/moon.rst b/keystone-moon/doc/source/extensions/moon/moon.rst
similarity index 100%
rename from keystone-moon/doc/source/extensions/moon.rst
rename to keystone-moon/doc/source/extensions/moon/moon.rst

diff --git a/keystone-moon/doc/source/extensions/moon_api.rst b/keystone-moon/doc/source/extensions/moon/moon_api.rst
similarity index 100%
rename from keystone-moon/doc/source/extensions/moon_api.rst
rename to keystone-moon/doc/source/extensions/moon/moon_api.rst