New Feature: Ignore Some Requests

Add 2 new options, ignore_localhost and ignore_hosts, which can ignore
requests so they aren't recorded in a cassette.

Closes #74

setup.py

@@ -43,7 +43,7 @@ setup(
         },
     install_requires=['PyYAML', 'contextdecorator', 'six'],
     license='MIT',
-    tests_require=['pytest', 'mock'],
+    tests_require=['pytest', 'mock', 'pytest-localserver'],
     cmdclass={'test': PyTest},
     classifiers=[
         'Development Status :: 4 - Beta',