Fix coverage story and add coveralls.io. (#85)

* Fix coverage story and add coveralls.io.

* Always be verbose to avoid failing builds because of 10 minutes without output.

* Add badges.

.coveragerc

+[run]
+source = BTrees
+
 [report]
 exclude_lines =
     # pragma: no cover

.travis.yml

@@ -13,11 +13,14 @@ matrix:
           python: 3.5
         - os: linux
           python: 3.6
-        - os: linux
-          python: 3.7-dev
+          env: WITH_COVERAGE=1
         - os: linux
           python: 3.6
-          env: PURE_PYTHON=1
+          env:
+            - PURE_PYTHON=1
+            - WITH_COVERAGE=1
+        - os: linux
+          python: 3.7-dev
         - os: linux
           python: pypy
         - os: linux
@@ -64,12 +67,19 @@ install:
     # (https://travis-ci.org/zopefoundation/BTrees/jobs/192340692) so
     # we install with pip manually.
     - pip install -U persistent
+    - if [[ "$WITH_COVERAGE" == "1" ]]; then pip install coveralls coverage; fi
     - pip install -e .[test,ZODB]
 script:
-    - zope-testrunner --test-path=. --auto-color --auto-progress
+    - |
+      if [[ "$WITH_COVERAGE" == "1" ]]; then
+        coverage run -m zope.testrunner --test-path=. --auto-color --auto-progress --verbose;
+      else
+        zope-testrunner --test-path=. --auto-color --auto-progress --verbose;
+      fi
 notifications:
     email: false
 after_success:
+    - if [[ "$WITH_COVERAGE" == "1" ]]; then coveralls; fi
     - echo [distutils]                                  > ~/.pypirc
     - echo index-servers = pypi                        >> ~/.pypirc
     - echo [pypi]                                      >> ~/.pypirc

README.rst

@@ -7,6 +7,18 @@
 .. image:: https://ci.appveyor.com/api/projects/status/github/zopefoundation/BTrees?branch=master&svg=true
     :target: https://ci.appveyor.com/project/mgedmin/BTrees
 
+.. image:: https://coveralls.io/repos/github/zopefoundation/BTrees/badge.svg?branch=master
+    :target: https://coveralls.io/github/zopefoundation/BTrees?branch=master
+
+.. image:: https://img.shields.io/pypi/v/BTrees.svg
+        :target: https://pypi.org/project/BTrees/
+        :alt: Current version on PyPI
+
+.. image:: https://img.shields.io/pypi/pyversions/BTrees.svg
+        :target: https://pypi.org/project/BTrees/
+        :alt: Supported Python versions
+
+
 This package contains a set of persistent object containers built around
 a modified BTree data structure.  The trees are optimized for use inside
 ZODB's "optimistic concurrency" paradigm, and include explicit resolution

tox.ini

@@ -37,10 +37,10 @@ deps =
 
 [testenv:coverage]
 basepython =
-    python2.7
+    python3.6
 commands =
     coverage run -m zope.testrunner --test-path=. --auto-color --auto-progress []
-    coverage report
+    coverage report --fail-under=92
 deps =
     {[testenv]deps}
     coverage