Add support for custom request matchers

This commit not only changes the default method of matching requests
(just match on method and URI instead of the entire request + headers)
but also allows the user to add custom matchers.

tests/integration/test_register_matcher.py

@@ -0,0 +1,32 @@
+import urllib2
+import vcr
+
+
+def true_matcher(r1, r2):
+    return True
+
+
+def false_matcher(r1, r2):
+    return False
+
+
+def test_registered_serializer_true_matcher(tmpdir):
+    my_vcr = vcr.VCR()
+    my_vcr.register_matcher('true', true_matcher)
+    testfile = str(tmpdir.join('test.yml'))
+    with my_vcr.use_cassette(testfile, match_on=['true']) as cass:
+        # These 2 different urls are stored as the same request
+        urllib2.urlopen('http://httpbin.org/')
+        urllib2.urlopen('https://httpbin.org/get')
+        assert len(cass) == 1
+
+
+def test_registered_serializer_false_matcher(tmpdir):
+    my_vcr = vcr.VCR()
+    my_vcr.register_matcher('false', false_matcher)
+    testfile = str(tmpdir.join('test.yml'))
+    with my_vcr.use_cassette(testfile, match_on=['false']) as cass:
+        # These 2 different urls are stored as different requests
+        urllib2.urlopen('http://httpbin.org/')
+        urllib2.urlopen('https://httpbin.org/get')
+        assert len(cass) == 2