[docs] add new rubric 'Source-Code'

- document namespace: searx.engines
- move docs/dev/xpath_engine.rst -> docs/src/searx.engines.xpath.rst

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/dev/index.rst

@@ -9,7 +9,6 @@ Developer documentation
    quickstart
    contribution_guide
    engine_overview
-   xpath_engine
    search_api
    plugins
    translation

docs/index.rst

@@ -35,5 +35,6 @@ anyone, you can set up your own, see :ref:`installation`.
    searx_extra/index
    utils/index
    blog/index
+   src/index
 
 .. _Searx-instances: https://searx.space

docs/src/index.rst

@@ -0,0 +1,14 @@
+===========
+Source-Code
+===========
+
+This is a partial documentation of our source code.  We are not aim to document
+every item from the source code, but we will add documentation when requested.
+
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Contents
+   :glob:
+
+   searx.*

docs/src/searx.engines.rst

@@ -0,0 +1,8 @@
+.. _load_engines:
+
+============
+Load Engines
+============
+
+.. automodule:: searx.engines
+  :members: