Improve documentation build (#539)

* use imgconverter
* enable pdf build with xelatex
* change heading levels
* restructure headings
* add chapter intro
* remove extensions from index

doc/index.rst

@@ -5,8 +5,15 @@
 
 .. include:: ../README.rst
 
+#######
 Content
--------
+#######
+
+User Documentation
+==================
+
+This chapter describes the central points that
+are relevant to the user of this library.
 
 .. toctree::
    :maxdepth: 1
@@ -19,13 +26,26 @@ Content
    user/usage
    user/barcode
 
+Printer profiles
+================
+
+This chapter gives a listing of the available
+printer profiles. Details are described in
+:ref:`capabilities-profile-intro`.
+
 .. toctree::
    :maxdepth: 1
    :caption: Printer profiles
 
-   printer_profiles/capabilities.rst
-   printer_profiles/available-profiles.rst
-   printer_profiles/available-encodings.rst
+   printer_profiles/capabilities
+   printer_profiles/available-profiles
+   printer_profiles/available-encodings
+
+Developer Documentation
+=======================
+
+This chapter summarizes information for
+developers of this library.
 
 .. toctree::
    :maxdepth: 1
@@ -36,6 +56,12 @@ Content
    dev/changelog
    dev/todo
 
+API Documentation
+=================
+
+This chapter contains an auto-generated
+documentation of the API of this library.
+
 .. toctree::
    :maxdepth: 1
    :caption: API Documentation
@@ -52,8 +78,9 @@ Content
    api/codepages
    api/katakana
 
+##################
 Indices and tables
-==================
+##################
 
 * :ref:`genindex`
 * :ref:`modindex`