SRC: Add APIs for querying required input and expected output frames.

* ma_resampler_get_required_input_frame_count()
  * ma_resampler_get_expected_output_frame_count()

These have not yet been implemented for the Speex backend.

This commit also adds an APIs for setting changing the rate:

  * ma_resampler_set_rate()
  * ma_resampler_set_rate_ratio()

miniaudio.h

@@ -4331,6 +4331,25 @@ static MA_INLINE float ma_scale_to_range_f32(float x, float lo, float hi)
 }
 
 
+/*
+Greatest common factor using Euclid's algorithm iteratively.
+*/
+static MA_INLINE ma_uint32 ma_gcf_u32(ma_uint32 a, ma_uint32 b)
+{
+    for (;;) {
+        if (b == 0) {
+            break;
+        } else {
+            ma_uint32 t = a;
+            a = b;
+            b = t % a;
+        }
+    }
+
+    return a;
+}
+
+
 /*
 Random Number Generation