Fix test method names

PEP8 says that method names should use lowercase_names.

test.py

@@ -9,7 +9,7 @@ import sys
 from doxygen import DoxyfileParse
 
 class TestParser(unittest.TestCase):
-    def testSimpleParse(self):
+    def test_simple_parse(self):
         text="""
 # comment
 INPUT  = test.h
@@ -17,7 +17,7 @@ INPUT  = test.h
         result = DoxyfileParse(text)
         self.assertEqual(["test.h"], result["INPUT"])
 
-    def testParseTagOnFirstLine(self):
+    def test_parse_tag_on_first_line(self):
         text="""INPUT=."""
         result = DoxyfileParse(text)
         self.assertEqual(["."], result["INPUT"])