Add python firmware server

Python firmware server can provide binary OTA images to Tasmota. See
README for usage. Tested on Linux.

api/fw-server.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+
+"""
+  fw-server.py - firmware server for Sonoff-Tasmota OTA upgrade
+
+  Copyright (C) 2018 Gennaro Tortone
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Requirements:
+   - Python3
+   - pip install netifaces flask
+
+Instructions:
+    Copy Sonoff-Tasmota firmware binary files in 'fw' directory.
+    A set of prebuilt files can be downloaded by Sonoff-Tasmota release page:
+        https://github.com/arendst/Sonoff-Tasmota/releases
+
+    Configure your Sonoff-Tasmota device with your fw-server URL:
+        Firmware Upgrade -> Upgrade by web server
+            http://<ip_address>:5000/sonoff-minimal.bin
+
+Usage:
+   ./fw-server.py -d <net_iface>   (default: eth0)
+
+Example:
+    ./fw-server.py -d wlan0
+"""
+
+import io
+import os.path
+from sys import exit
+from flask import Flask, send_file
+from optparse import OptionParser
+import netifaces as ni
+
+parser = OptionParser()
+parser.add_option("-d", "--dev", action="store", type="string",
+                  dest="netdev", default="eth0", help="network interface (default: eth0)")
+(options, args) = parser.parse_args()
+
+try:
+    netip = ni.ifaddresses(options.netdev)[ni.AF_INET][0]['addr']
+except Exception as e:
+    print("E: network interface error - {}".format(e))
+    exit(1)
+
+app = Flask(__name__)
+
+@app.route('/<filename>')
+def fw(filename):
+   if(os.path.exists("fw/" + str(filename))):
+      return send_file("fw/" + str(filename), attachment_filename=filename, mimetype='application/octet-stream')
+   else:
+      return("ERROR: file not found")
+
+if __name__ == "__main__":
+    try:
+        app.run(host=netip)
+    except Exception as e:
+        print("E: {}".format(e))

api/fw/README

@@ -0,0 +1,3 @@
+Copy Sonoff-Tasmota firmware binary files in this directory.
+A set of prebuilt files can be downloaded by Sonoff-Tasmota release page:
+https://github.com/arendst/Sonoff-Tasmota/releases