c89 compliant? (#237)

* Replace C++ comments into  C comments

* Move INLINE out of Makefile.common, move to fceu-types.h

An INLINE define is still existing in Makefile.common for msvc (dont
have a way to to test that). Moved the rest into fceu-types.h using the
one already existing from emu2413.h.

* Increase maximum volume for apu channels

src/boards/emu2413.h

@@ -7,20 +7,6 @@
 #include <math.h>
 #include "../fceu-types.h"
 
-#ifndef INLINE
-
-#if defined(_MSC_VER)
-#define INLINE __forceinline
-#elif defined(__GNUC__)
-#define INLINE __inline__
-#elif defined(_MWERKS_)
-#define INLINE inline
-#else
-#define INLINE
-#endif
-#endif
-
-
 #ifdef __cplusplus
 extern "C" {
 #endif