Enable coverage testing, report with codecov

We run coverage tests only in py3.6

.codecov.yml

@@ -0,0 +1,11 @@
+coverage:
+  precision: 0
+  round: down
+  status:
+    patch:
+      default:
+        target: 97
+    project:
+      default:
+        threshold: 1%
+comment: false

.gitignore

@@ -50,3 +50,7 @@ doc/source/_build/
 
 # Files generated by setupegg.py
 mpmath.egg-info/
+
+# Coverage-related files
+.coverage
+htmlcov/

.travis.yml

@@ -5,16 +5,25 @@ python:
   - 3.3
   - 3.4
   - 3.5
-  - 3.6
   - 3.7-dev
   - pypy
   - pypy3.5
+matrix:
+  include:
+    - python: 3.6
+      env: COVERAGE='on'
 install:
   - pip install -e .[develop]
 script:
   # Guard against invalid escapes in strings, like '\s'.
   - python -We:invalid -m compileall -f mpmath -q
   - pycodestyle
-  - py.test
+  - |
+    if [ -n "${COVERAGE}" ]; then
+      py.test --cov mpmath
+    else
+      py.test
+    fi
+after_success: test -n "${COVERAGE}" && codecov
 notifications:
   email: false

setup.cfg

@@ -32,6 +32,8 @@ tests_require = mpmath[tests]
 tests = pytest
 develop = %(tests)s
           pycodestyle
+          pytest-cov
+          codecov
 [pycodestyle]
 select = E101,W191,W291,W293,E111,E112,E113,W292,W391
 [tool:pytest]
@@ -39,3 +41,6 @@ addopts = --doctest-modules
           --ignore=setup.py
           --doctest-glob='*.txt'
 norecursedirs = doc/source/plots demo
+[coverage:run]
+branch = True
+omit = mpmath/tests/*