Merge pull request #5217 from jreback/cacher

BUG: don't try to deal with a dead cache referant (GH5216)
DOC: add DataFrame et al class docstring to api docs

+ add template class.rst (copied from numpy)
+ adapt sphinxext numpydoc (was outdated, attributes not included)
Merge pull request #5160 from jorisvandenbossche/api-docs-template

DOC: add DataFrame et al class docstring to api docs
API: rename _prop_attributes to __finalize__ (in NDFrame)
     rename _propogate_attributes to _metadata (in NDFrame)
     change methods which directly pass metadata to use __finalize__

     These provide a simple mechanism for meta data propagation, which
     can be overriden in subclasses if desired