Allow suiteSetUp() and suiteTearDown() to be provided as normal C functions.

This is simpler and more flexible than embedding C code in the Ruby options
(:suite_setup and :suite_teardown).  However, support for :suite_setup and
:suite_teardown is kept for backwards compatibility.

Several configurations are possible:
1. :suite_setup and :suite_teardown options provided and used.
2. :suite_setup and :suite_teardown options not provided (nil):
  2a. Weak symbols not supported; suiteSetUp() and suiteTearDown() are not called.
      It would be simpler to make user-provided functions mandatory in this case,
      but it could break some pre-existing test suites.
  2b. Weak symbols are supported and the stub implementations of suiteSetUp() and
      suiteTearDown() are called if there are no user-provided functions.
  2c. Weak symbols are supported but overridden by user-provided suiteSetUp() and
      suiteTearDown() functions.

src/unity.h

@@ -15,9 +15,20 @@ extern "C"
 
 #include "unity_internals.h"
 
+/* These functions are intended to be called before and after each test.  Unity
+ * provides stub implementations annotated as weak symbols (if supported by the
+ * compiler). */
 void setUp(void);
 void tearDown(void);
 
+/* These functions are intended to be called at the beginning and end of an
+ * entire test suite.  suiteTearDown() is passed the number of tests that
+ * failed, and its return value becomes the exit code of main().  Unity
+ * provides stub implementations annotated as weak symbols (if supported by the
+ * compiler). */
+void suiteSetUp(void);
+int suiteTearDown(int num_failures);
+
 /*-------------------------------------------------------
  * Configuration Options
  *-------------------------------------------------------