Add an option to omit UNITY_OUTPUT_CHAR declaration from the header

This solves the warnings from -Wredundant-decls when overriding the
  OUTPUT function with a function declared in another header.
 It's better this is the non-default option, since using it requires either
  a declaration of the new function OR a preprocessor guard on declaring
  UNITY_OUTPUT_CHAR (as in unity.c here), in every file using the function.
 See Pull Request #185 for more.

.travis.yml

@@ -6,4 +6,4 @@ script:
   - cd test && rake ci
   - make -s
   - cd ../extras/fixture/test && rake ci
-  - make -s default noStdLibMalloc
+  - make -s default noStdlibMalloc

src/unity.c

@@ -7,6 +7,9 @@
 #include "unity.h"
 #include <stddef.h>
 
+#ifdef UNITY_OMIT_OUTPUT_CHAR_HEADER_DECLARATION
+int UNITY_OUTPUT_CHAR(int); //If omitted from header, declare it here so it's ready for use
+#endif
 #define UNITY_FAIL_AND_BAIL   { Unity.CurrentTestFailed  = 1; longjmp(Unity.AbortFrame, 1); }
 #define UNITY_IGNORE_AND_BAIL { Unity.CurrentTestIgnored = 1; longjmp(Unity.AbortFrame, 1); }
 /// return prematurely if we are already in failure or ignore state

src/unity_internals.h

@@ -293,7 +293,9 @@ typedef UNITY_DOUBLE_TYPE _UD;
 #define UNITY_OUTPUT_CHAR(a) putchar(a)
 #else
 //If defined as something else, make sure we declare it here so it's ready for use
+  #ifndef UNITY_OMIT_OUTPUT_CHAR_HEADER_DECLARATION
 extern int UNITY_OUTPUT_CHAR(int);
+  #endif
 #endif
 
 #ifndef UNITY_PRINT_EOL