eliminate bifurcated rw lock path based on exclusive mode; promote thread operations to base layer, use os layer as impl; first pass on moving file streaming layer to base layer's async wavefront

src/base/base_inc.c

@@ -12,7 +12,7 @@
 #include "base_arena.c"
 #include "base_math.c"
 #include "base_strings.c"
-#include "base_sync.c"
+#include "base_threads.c"
 #include "base_thread_context.c"
 #include "base_command_line.c"
 #include "base_markup.c"