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/fceu-types.h

@@ -53,6 +53,19 @@ typedef unsigned long long uint64;
 typedef long long int64;
 #endif
 
+#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
+
 #if PSS_STYLE == 2
 
 #define PSS "\\"