* Fix documentation about type alias edge_size_type -> edges_size_type
This replaces occurences of `edge_size_type` (sg.) in the documentation
with the actual `edges_size_type` (pl.) as it is named in the
implementation.
There is a graph implementation (Stanford graph) that has a type alias
of `edge_size_type` (sg.) --- I did not change that implementation, as
it would break backwards compatibility, and therefore I also did not
change its documentation.
* Fix documentation on push_relabel algorithm, defined in header: preflow_push -> push_relabel
