Add a facility to control tracing without recompiling

This will help greatly when it comes to diagnosing customer issues.
diff --git a/build.json b/build.json
index fca6578..172753b 100644
--- a/build.json
+++ b/build.json
@@ -32,6 +32,7 @@
         "src/core/channel/noop_filter.h",
         "src/core/compression/algorithm.h",
         "src/core/compression/message_compress.h",
+        "src/core/debug/trace.h",
         "src/core/httpcli/format_request.h",
         "src/core/httpcli/httpcli.h",
         "src/core/httpcli/httpcli_security_context.h",
@@ -124,6 +125,7 @@
         "src/core/channel/noop_filter.c",
         "src/core/compression/algorithm.c",
         "src/core/compression/message_compress.c",
+        "src/core/debug/trace.c",
         "src/core/httpcli/format_request.c",
         "src/core/httpcli/httpcli.c",
         "src/core/httpcli/httpcli_security_context.c",