Z2AudioLib: Migrate declarations out of functions.h to respective files (#96)

Removes the strong dependency on a single header file and moves
declarations to their respective header file.

This allows for making dependencies explicit in cpp files and other
headers, and also makes it much easier to track where everything related
to a particular component is.

This change also creates a few header files that previously didn't
exist, making it much nicer for people implementing things, as they
won't need to create the header file, it'll just be there ready to go.

Ideally functions.h wouldn't even be a thing, as this header adds a lot
of preprocessing overhead due to its size, and will continue to grow
significantly larger over the lifespan of the project, which can also
impact the performance of editors that do dependency lookups and
context-aware syntax highlighting.

include/Z2AudioLib/Z2Calc/Z2Calc.h

@@ -1,3 +1,6 @@
+#ifndef Z2CALC_H_
+#define Z2CALC_H_
+
 #include "JSystem/JMath/random.h"
 #include "global.h"
 
@@ -23,3 +26,16 @@ float getParamByExp(float, float, float, float, float, float, Z2Calc::CurveSign)
 float getRandom(float, float, float);
 float getRandom_0_1(void);
 }  // namespace Z2Calc
+
+extern "C" {
+void calcNoise1f__Q26Z2Calc8FNoise1fFv(void);
+void getRandom__6Z2CalcFfff(void);
+void getRandom_0_1__6Z2CalcFv(void);
+void getParamByExp__6Z2CalcFffffffQ26Z2Calc9CurveSign(void);
+void linearTransform__6Z2CalcFfffffb(void);
+void setParam__Q26Z2Calc8FNoise1fFfff(void);
+
+void Z2Calc_NS_linearTransform(void);
+}
+
+#endif  // Z2CALC_H_