documentation (#79)

Documentation for operator.py, span.py, plotter.py. 
Co-authored-by: Dario Coscia <dariocoscia@dhcp-128.eduroam.sissa.it>

docs/source/_rst/code.rst

@@ -4,8 +4,11 @@ Code Documentation
 .. toctree::
     :maxdepth: 3
 
+    PINN <pinn.rst>
     LabelTensor <label_tensor.rst>
+    Span <span.rst>
     FeedForward <fnn.rst>
     DeepONet <deeponet.rst>
-    PINN <pinn.rst>
     ContinuousConv <convolution.rst>
+    Operators <operators.rst>
+    Plotter <plotter.rst>

docs/source/_rst/operators.rst

@@ -0,0 +1,10 @@
+Operators
+===========
+.. currentmodule:: pina.operators
+
+.. automodule:: pina.operators
+    :members:
+    :private-members:
+    :undoc-members:
+    :show-inheritance:
+    :noindex:

docs/source/_rst/plotter.rst

@@ -0,0 +1,8 @@
+Plotter
+===========
+.. currentmodule:: pina.plotter
+
+.. automodule:: pina.plotter
+    :members:
+    :show-inheritance:
+    :noindex:

docs/source/_rst/span.rst

@@ -0,0 +1,10 @@
+Span
+===========
+.. currentmodule:: pina.span
+
+.. automodule:: pina.span
+
+.. autoclass:: Span
+    :members:
+    :show-inheritance:
+    :noindex: