Add heartbeat to API

webif/html/api/heartbeat.jim

@@ -0,0 +1,17 @@
+#!/mod/bin/jimsh
+source /mod/webif/lib/setup
+require system.class
+package require json
+
+httpheader {application/json}
+
+set time [clock milliseconds]
+
+catch {
+	lappend vars \
+		isotime [system isotime $time] \
+		timestamp $time \
+		uptime [system uptime]
+
+	puts [json::encode $vars obj]
+}