docs: Add "reference" directory for putting docs about the language.

docs/esp8266_contents.rst

@@ -4,4 +4,5 @@ MicroPython documentation contents
 .. toctree::
 
     library/index.rst
+    reference/index.rst
     license.rst

docs/pyboard_contents.rst

@@ -7,6 +7,7 @@ MicroPython documentation contents
     pyboard/general.rst
     pyboard/tutorial/index.rst
     library/index.rst
+    reference/index.rst
     pyboard/hardware/index.rst
     license.rst
 

docs/reference/index.rst

+The MicroPython language
+========================
+
+MicroPython aims to implement the Python 3.4 standard, and most of
+the features of MicroPython are identical to those described by the
+documentation at
+`docs.python.org <https://docs.python.org/3.4/reference/index.html>`_.
+
+Differences to standard Python as well as additional features of
+MicroPython are described in the sections here.

docs/topindex.html

@@ -47,6 +47,10 @@
       </p>
     </td>
     <td width="40%" style="padding-left:2em;">
+      <p class="biglink">
+        <a class="biglink" href="{{ pathto("reference/index") }}">Language Reference</a><br/>
+        <span class="linkdescr">information about MicroPython specific language features</span>
+      </p>
       {% if port == "pyboard" %}
         <p class="biglink">
             <a class="biglink" href="{{ pathto(port + "/hardware/index") }}">The {{ port }} hardware</a><br/>

docs/wipy_contents.rst

@@ -6,4 +6,5 @@ MicroPython documentation contents
     wipy/quickref.rst
     wipy/general.rst
     library/index.rst
+    reference/index.rst
     license.rst