lxml is no longer used

Remove from requirements and installation docs

Related: #241

documentation/src/install.rst

@@ -19,11 +19,6 @@ Markdown
 :code:`Markdown` (package name may be :code:`python-markdown` or
 :code:`python3-markdown`) is used to format the description texts.
 
-LXML
-....
-
-:code:`lxml` (package name may be :code:`python-lxml` or :code:`python3-lxml`)
-is needed for the Inkscape plugin.
 
 setuptools
 ..........

documentation/src/install/macos.rst

@@ -31,7 +31,7 @@ General
 
    .. code::
 
-      pip3 install Markdown lxml affine
+      pip3 install Markdown affine
 
 4. Download Boxes.py via Git:
 

documentation/src/install/windows.rst

@@ -27,7 +27,7 @@ Following steps are known to work under Windows 10 (64-bit):
        :alt: Screenshot of Python 3.7 (64-bit) installer with PATH checked
        :align: center
 
-3.  Run the command :code:`pip install Markdown lxml affine`
+3.  Run the command :code:`pip install Markdown affine`
     (Note: If the command pip is not found, you probably forgot to add the
     Python installation to the PATH environment variable in step 2)
 	       

requirements.txt

@@ -1,5 +1,4 @@
 affine
 markdown
-lxml
 setuptools
-sphinx
+sphinx