Add support for Billion / Telewell devices

```
Please investigate the work previously done by Finnish hacker Harry Sintonen
considering the violations of GPL by Telewell and Billion (same devices,
rebranding):

https://www.sintonen.fi/telewell_gpl/

Especially, read https://www.sintonen.fi/telewell_gpl/readme.txt,
https://www.sintonen.fi/telewell_gpl/gpl_components_in_firmware.txt and
https://www.sintonen.fi/telewell_gpl/gpl_components_in_firmware2.txt.

Sintonen provides public domain source code for extracting these firmwares
(cramfs and kernel).

Thanks to Sintonen, Telewell has provided (at least almost) everything required
to build the firmware:
https://www.telewell.fi/edistyneille/

Billion has also provided some source packages, e.g.:
http://au.billion.com/downloads/usermanual/wireless/PCRange-7300GA-V1.35-RC8-180
-80.3.tar.gz,
http://au.billion.com/downloads/firmware/wireless/PCRange7800NL.rar,
http://au.billion.com/downloads/firmware/3g-adsl2+/7800GZ_1.04a_PCRange.tar.gz,
http://au.billion.com/downloads/firmware/wireless/7300N_1.06g_PCRange.tar.gz.
Could issue 93 also be solved with these?

Downloading the links on that page will give you the sources + toolchains. I've
managed to build the firmware package from sources for TW-EA510 v3. The process
is quite straight forward, but will most likely require a few Makefile changes
(sed path etc).

As Sintonen provides working code for extracting the firmware and the method
for packaging the firmware is included in the toolchain, this should be quite
easy task for you?

If you are willing to act on this, I've got a TW-EA510 v3 (b) and a TTL serial
for testing purposes. However, this specific firmware
(https://telewell.fi/files/paivitystiedostot/Telewell-510v3b-1_08a_dj5-A_afw.zip
) is not being fully understood by Sintonen's tools as only the kernel image is
extracted by scangzip.
```

Original issue reported on code.google.com by `joe.ka...@gmail.com` on 10 Jul 2013 at 10:52

Start by reading the linked Sintonen README and firmware component notes, then inspect the existing scangzip extraction path and packaging workflow. Test against the Telewell TW-EA510 v3(b) firmware and the available source packages; done means the relevant Billion and Telewell images can be extracted and rebuilt, with testing on the supplied hardware.

Written by the indexing model from the issue text.