add support to build sensors from json

Add support to build sensors from a json configuration file.

Change-Id: Ic5bcbcd01e085ab0d4efaed314af8dc7e82b0b9d
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index 914c558..09a52d5 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -63,6 +63,7 @@
 	sensors/host.cpp \
 	sensors/builder.cpp \
 	sensors/builderconfig.cpp \
+	sensors/buildjson.cpp \
 	sensors/manager.cpp \
 	pid/ec/pid.cpp \
 	pid/ec/stepwise.cpp \