realtime-voice-conversion based on last year's work

This is based on the work I did in (July - October)ish 2019 to get real
time voice conversion working. I've removed it from the `voder` library
and made it into an isolable program. I'll work on extending the
capabilities.

protos/audio.proto

@@ -0,0 +1,64 @@
+syntax = "proto3";
+package voder_audio;
+
+message VocodeAudioRequest {
+  repeated float float_audio = 1;
+
+  // An autoincrement sent with each request.
+  int64 request_batch_number = 2;
+
+  message VocodeParams {
+    // The initial sample rate coming from the microphone.
+    int32 initial_sample_rate = 1;
+
+    // Original sample
+    int32 original_source_rate = 9;
+    bool original_source_save_file = 10;
+
+    // Resample before passing to the algorithm?
+    bool pre_convert_resample = 2;
+    int32 pre_convert_resample_rate = 3;
+    bool pre_convert_resample_save_file = 4;
+
+    // The hard-coded hyperparameter of the model.
+    // Probably don't want to change from 16000.
+    int32 model_hyperparameter_sampling_rate = 5;
+    bool model_save_file = 11;
+
+    // Resample after passing to the algorithm?
+    bool post_convert_resample = 6;
+    int32 post_convert_resample_rate = 7;
+    bool post_convert_resample_save_file = 8;
+  }
+
+  VocodeParams vocode_params = 10;
+
+  // We'll resend these params for every batch, but will only use
+  // the last batch's settings. Kind of a dumb API, but it'll work.
+  //int32 sample_rate = 2;
+
+  //bool skip_resample = 3;
+  bool skip_vocode = 4;
+
+  // Debugging
+  //bool save_files = 5;
+
+  // How big we let the buffer grow before running 'convert'.
+  int32 buffer_size_minimum = 6;
+
+  // Requested output rate
+  //int32 output_rate = 7;
+
+  // Discard the vocoded audio and return the original
+  bool discard_vocoded_audio = 8;
+
+  // Rate param for the model
+  //int32 model_sampling_rate = 9;
+}
+
+message VocodeAudioResponse {
+  repeated float float_audio = 1;
+
+  // A sidecar-side autoincrement sent with each request.
+  int64 response_batch_number = 2;
+}