Option to omit UnityBegin/UnityEnd calls in generate_test_runner

By passing --omit_begin_end=1 to generate_test_runner.rb, the script
will now omit calls to UnityBegin and UnityEnd when running tests in a
suite.

This allows multiple suites to be executed in a row, and then have an overall
summary of the tests which were executed across all suites.

src/unity.c

@@ -1824,6 +1824,12 @@ void UnityDefaultTestRun(UnityTestFunction Func, const char* FuncName, const int
     UnityConcludeTest();
 }
 
+/*-----------------------------------------------*/
+void UnitySetTestFile(const char* filename)
+{
+	Unity.TestFile = filename;
+}
+
 /*-----------------------------------------------*/
 void UnityBegin(const char* filename)
 {