Convert .ino -> .cpp (#2228)

- general conversion from .ino modules into a separate .cpp files
- clean-up internal headers, place libraries into .h. guard .cpp with _SUPPORT flags 
- fix some instances of shared variables instead of public methods
- tweak build system to still build a single source file via os environment variable ESPURNA_BUILD_SINGLE_SOURCE

code/espurna/netbios.cpp

@@ -0,0 +1,20 @@
+/*
+
+NETBIOS MODULE
+
+Copyright (C) 2017-2019 by Xose Pérez <xose dot perez at gmail dot com>
+
+*/
+
+#include "netbios.h"
+
+#if NETBIOS_SUPPORT
+
+void netbiosSetup() {
+    static WiFiEventHandler _netbios_wifi_onSTA = WiFi.onStationModeGotIP([](WiFiEventStationModeGotIP ipInfo) {
+        NBNS.begin(getSetting("hostname").c_str());
+        DEBUG_MSG_P(PSTR("[NETBIOS] Configured\n"));
+    });
+}
+
+#endif // NETBIOS_SUPPORT