Improvements to the execution time feature

- Running time macros have been made more portable, previously it was not
  possible to override all macros
- Running time macros will be executed by default test runner, and auto test
  runners
- Adds a default execution time implementation for unix. (Previous default
  implementation only worked on Windows)
- For embedded platforms there is a simple method of getting a default
  implementation by defining a single macro UNITY_CLOCK_MS()
- Removed need for UNITY_EXEC_TIME_RESET. This was not being used for the default
  implementations, if anything ever did need reset-like functionality it could
  simply be wrapped up with the start or stop macros for that platform

test/tests/testunity.c

@@ -104,8 +104,8 @@ void testUnitySizeInitializationReminder(void)
         UNITY_COUNTER_TYPE CurrentTestFailed;
         UNITY_COUNTER_TYPE CurrentTestIgnored;
 #ifdef UNITY_INCLUDE_EXEC_TIME
-        UNITY_COUNTER_TYPE CurrentTestStartTime;
-        UNITY_COUNTER_TYPE CurrentTestStopTime;
+        UNITY_TIME_TYPE CurrentTestStartTime;
+        UNITY_TIME_TYPE CurrentTestStopTime;
 #endif
 #ifndef UNITY_EXCLUDE_SETJMP_H
         jmp_buf AbortFrame;