minor doc changes in bag.core (#2797)
minor doc changes in bag.core (#2797)

* minor doc changes in bag.core

Fixed some formatting and other very minor things

* added periods

* Update core.py

* removed whitespace

blaze/dask,ContinuumIO/dask,dask/dask,ContinuumIO/dask,jcrist/dask,jcrist/dask,blaze/dask,mrocklin/dask,dask/dask,mrocklin/dask,jakirkham/dask,jakirkham/dask