removed power_indices documentation and other minor changes

sphinx/source/field.rst

@@ -3,6 +3,9 @@
 The ``Field`` class -- Basic class to define fields over spaces
 ...............................................................
 
+The discrete representation of a continuous field over multiple spaces.
+
+In NIFTY, Fields are used to store data arrays and carry all the needed metainformation (i.e. the domain) for operators to be able to work on them. In addition Field has methods to work with power-spectra.
 
 .. autoclass:: Field
     :show-inheritance:

sphinx/source/power_indices.rst

-.. currentmodule:: nifty
-
-The ``PowerIndices`` class --  Useful set of indices for the PowerSpace
-.......................................................................
-
-.. autoclass:: PowerIndices
-    :show-inheritance:
-    :members:

sphinx/source/spaces.rst

@@ -19,7 +19,6 @@ Next to the generic :py:class:`Space` class, NIFTY has implementations of five s
     gl_space
     lm_space
     power_space
-    power_indices
 
 .. currentmodule:: nifty