ENH: add coverage info with coveralls.io for Travis runs.
BUG: coverage didn't run on Travis, try again.
BUG: next try to fix coverage run.
MAINT: add .coveragerc file to limit content of .coverage file to scipy.

Also add a Coveralls badge next to the Travis CI one in README.txt
Merge pull request #2907 from rgommers/coverage-dot-io

MAINT: add coverage info with coveralls.io for Travis runs.