The file always exist so no need to do '-include'.

Replaced using:

    sed -i 's|-\(include $(RIOTCPU)/.*/Makefile.features\)|\1|' \
        $(git grep -l  '$(RIOTCPU)/.*/Makefile.features' boards)

- Use RIOT's GPIO interface to access the sensor to increase portability
- Changed API to allow more than one sensor per board
- Added `sht1x_params.h` that specifies how the sensors is connected - each
  board can overwrite default settings by #defining SHT1X_PARAM_CLK and
  SHT1X_PARAM_DATA
- Changed arithmetic to use integer calculations only instead of floating point
  arithmetic
- Added support for checking the CRC sum
- Allow optional skipping of the CRC check to speed up measuring
- Added support for advanced features like reducing the resolution and skipping
  calibration to speed up measuring
- Allow specifying the supply voltage of sensor which heavily influences the
  temperature result (and use that information to calculate the correct
  temperature)
- Reset sensor on initialization to bring it in a well known state
- Support for the obscure heater feature. (Can be useful to check the
  temperature sensor?)
- Updated old SHT11 shell commands to the new driver interface, thus allowing
  more than one SHT10/11/15 sensor to be used
- Added new shell command to allow full configuration of all attached SHT1x
  sensors
- Removed old command for setting the SHT11 temperature offset, as this feature
  is implemented in the new configuration command

This feature is already defined by the (common) CPU implementation,
so no need to re-define it for each board.

- adapted the SPI driver
- adapted all boards using the CPU

- renamed board-conf.h to board_common.h
- moved common defines to board_common.h

Add reference URL, fix typos.

fixed indention and parens for LED defines

* also added a trailing underscore to header guards for consistency

Commit for PR 2623, repairing header file include guards.
This PR is intended to fix the include guards in files under RIOT/boards

SQUASH ME: fix underscore removal overdos

SQUASH ME: consistent macro naming

SQUASH ME: missed that one

SQUASH ME: fixed overdo

SQUASH ME: consistency