Reads the file
filename containing graph edges in TSV format.
Name of a TSV file specifying the edges of a graph. Each line of
the input file should be the specification of a single graph edge in the
source\<TAB\>target[\<TAB\>weight]. If supplied,
be a floating point number; if not supplied, it defaults to 1.0. Multiple
edges between the same source and target node IDs are combined by picking
the edge with the largest weight.
A graph represented as a
dict: source -> (target -> weight).