add coverage make target

AUTHORS.rst

@@ -142,3 +142,4 @@ Patches and Suggestions
 - Can Ibanoglu <can.ibanoglu@gmail.com> @canibanoglu
 - Thomas Weißschuh <thomas@t-8ch.de> @t-8ch
 - Jayson Vantuyl <jayson@aggressive.ly> @kagato
+- Pengfei.X <pengphy@gmail.com>

Makefile

@@ -4,6 +4,9 @@ init:
 test:
 	py.test
 
+coverage:
+	py.test --verbose --cov-report term --cov=requests test_requests.py
+
 ci: init
 	py.test --junitxml=junit.xml
 

requirements.txt

@@ -1,4 +1,5 @@
 py==1.4.12
 pytest==2.3.4
+pytest-cov==1.6
 invoke==0.2.0
 wheel