Add battery.charge to hunnox driver

[rtm516]

This adds battery.charge to the hunnox driver as used by Powercool UPS devices. Tested with a real device and works well.

Tested Device: PowerCool 1500 VA (Rack)

After this PR, as you can see battery.charge is included

battery.charge: 100
battery.voltage: 27.4
device.type: ups
driver.debug: 5
driver.flag.allow_killpower: 0
driver.flag.norating: enabled
driver.flag.noscanlangid: enabled
driver.flag.novendor: enabled
driver.name: nutdrv_qx
driver.parameter.langid_fix: 0x0409
driver.parameter.pollfreq: 30
driver.parameter.pollinterval: 2
driver.parameter.port: auto
driver.parameter.productid: 0000
driver.parameter.protocol: hunnox
driver.parameter.synchronous: auto
driver.parameter.vendorid: 0001
driver.state: dumping
driver.version: 2.8.4.1
driver.version.data: Hunnox 0.03
driver.version.internal: 0.48
driver.version.usb: libusb-1.0.27 (API: 0x0100010A)
input.frequency: 49.9
input.voltage: 244.0
input.voltage.fault: 0.0
output.voltage: 244.0
ups.beeper.status: disabled
ups.delay.shutdown: 60
ups.delay.start: 0
ups.load: 0
ups.productid: 0000
ups.status: OL
ups.temperature: 29.0
ups.type: offline / line interactive
ups.vendorid: 0001

General points

• Described the changes in the PR submission or a separate issue, e.g.
  known published or discovered protocols, applicable hardware (expected
  compatible and actually tested/developed against), limitations, etc.

• There may be multiple commits in the PR, aligned and commented with
  a functional change. Notably, coding style changes better belong in a
  separate PR, but certainly in a dedicated commit to simplify reviews
  of "real" changes in the other commits. Similarly for typo fixes in
  comments or text documents.

• Please star NUT on GitHub, this helps with sponsorships! ;)

Frequent "underwater rocks" for driver addition/update PRs

• Revised existing driver families and added a sub-driver if applicable
  (nutdrv_qx, usbhid-ups...) or added a brand new driver in the other
  case.

• Did not extend obsoleted drivers with new hardware support features
  (notably blazer and other single-device family drivers for Qx protocols,
  except the new nutdrv_qx which should cover them all).

• For updated existing device drivers, bumped the DRIVER_VERSION macro
  or its equivalent.

• For USB devices (HID or not), revised that the driver uses unique
  VID/PID combinations, or raised discussions when this is not the case
  (several vendors do use same interface chips for unrelated protocols).

• For new USB devices, built and committed the changes for the
  scripts/upower/95-upower-hid.hwdb file

• Proposed NUT data mapping is aligned with existing docs/nut-names.txt
  file. If the device exposes useful data points not listed in the file, the
  experimental.* namespace can be used as documented there, and discussion
  should be raised on the NUT Developers mailing list to standardize the new
  concept.

• Updated data/driver.list.in if applicable (new tested device info)

Frequent "underwater rocks" for general C code PRs

• Did not "blindly assume" default integer type sizes and value ranges,
  structure layout and alignment in memory, endianness (layout of bytes and
  bits in memory for multi-byte numeric types), or use of generic int where
  language or libraries dictate the use of size_t (or ssize_t sometimes).

• Progress and errors are handled with upsdebugx(), upslogx(),
  fatalx() and related methods, not with direct printf() or exit().
  Similarly, NUT helpers are used for error-checked memory allocation and
  string operations (except where customized error handling is needed,
  such as unlocking device ports, etc.)

• Coding style (including whitespace for indentations) follows precedent
  in the code of the file, and examples/guide in docs/developers.txt file.

• For newly added files, the Makefile.am recipes were updated and the
  make distcheck target passes.

General documentation updates

• Updated docs/acknowledgements.txt (for vendor-backed device support)

• Added or updated manual page information in docs/man/*.txt files
  and corresponding recipe lists in docs/man/Makefile.am for new pages

• Passed make spellcheck, updated spell-checking dictionary in the
  docs/nut.dict file if needed (did not remove any words -- the make
  rule printout in case of changes suggests how to maintain it).

Additional work may be needed after posting this PR

• Propose a PR for NUT DDL with detailed device data dumps from tests
  against real hardware (the more models, the better).

• Address NUT CI farm build failures for the PR: testing on numerous
  platforms and toolkits can expose issues not seen on just one system.

• Revise suggestions from LGTM.COM analysis about "new issues" with
  the changed codebase.

[jimklimov]

Looks nice, thanks!

[AppVeyorBot]

❌ Build nut 2.8.4.3958-master failed (commit dae41ce65c by @rtm516)

[AppVeyorBot]

✅ Build nut 2.8.4.3959-master completed (commit 7456f538bd by @rtm516)