Allow flashing with an offset in ROM from the rom base address.
It reuses `IMAGE_OFFSET` configuration variable name from `openocd.sh`.

This will allow flashing multiple images with different flash operations.

This mimics openocd behaviour that only erase needed sectors of the rom.

 dist: move testrunner to pythonlibs as package 

pkg: cmsis-dsp: fix -Wunknown-attributes for LLVM

Apparently LLVM doesn't know the `optimize` attribute.

boards/sensebox: Add support for SenseBox board

make: Makefile.include: Remove -Wno-implicit-fallthrough

frdm-k64f: Add SAUL ADC configuration

frdm-k64f: Update ADC configuration 

cpu/lpc2387: Fixed documentation and bugs preventing use of LLVM

pkg/ccn-lite/relic: check for minimal cmake version

- Previous cast was to a function pointer was not legal
- Using already present function pointer to store the IAP entry point to improve
  readability. (Which also fixes the cast issue.)

relic does not build with cmake < 3.6.0. This checks for a minimal version
instead of failing to compile.

    cmake version 3.5.2 is not >= to minimal required 3.6.0

    Makefile:25: recipe for target '..cmake_version_supported' failed

ccn-lite does not build with cmake < 3.6.0. This checks for a minimal version
instead of failing to compile.

    cmake version 3.5.2 is not >= to minimal required 3.6.0

    Makefile:25: recipe for target '..cmake_version_supported' failed

Tested with versions 3.5.2, 3.6.0-rc1, 3.6.0, 3.6.3, 3.7.0-rc1, 3.7.0.

Note: the check used does not consider '-rcX' as 'sort -V' does not handle them
properly.

    usage: has_minimal_version.sh <version> <minimal_version> [toolname]
      Checks that version >= minimal_version
      Version format MAJOR.MINOR.PATCH ex 3.1.4

gnrc/6lo: Set more data flag on all but last fragment

stm32_common/eeprom: fix DEBUG formatting

This fixes compilation for `periph_eeprom` with LLVM/clang and also is
more in accordance with our [coding conventions].

[coding conventions]: https://github.com/RIOT-OS/RIOT/wiki/Coding-conventions#-wformat

boards: slstk3402a: add i2c

- arm_reset was completely undocumented, even though technical details buried
  deeply in the data sheet of the LPC2387 are involved in the code
- The attribute "naked" is misplaced, it should only be used when no C code
  is present. However, the function consists of C code only
- The attribute "noreturn" has to be used in the declaration [1] of a function,
  not in the implementation. Otherwise the caller is not informed and code using
  the function will not be optimized.

[1]: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html

kinetis: timer: #ifdef unused functions

Another issue revealed by compiling several apps with LLVM/clang for
the `teensy31` board.

cpu/nrf51: fix formatting uint to PRIu32

Release notes for 2018.07

This release-notes where contributed by the following github users:

* aabadie
* bergzand
* cladmi
* gebart
* miri64
* PeterKietzmann

Testrunner is now impported as a package found in PYTHONPATH, so
import can be placed at the top of the script as usual.

os package is imported by every test script but only used by
a few, thus flake8 check reported errors.

Remove now obsolete sys.append from all tests, as testrunner was moved
to dist/pythonlibs as proper package.

As testrunner is moved to dist/pythonlibs which is exported
via PYTHONPATH, testrunner is found by all test scripts.

pkg: update ccn-lite and adapt shell commands

gnrc_netif_ieee802154: Set FCF Frame Pending when more data is expected

gnrc_netif: Introduce GNRC_NETIF_HDR_FLAGS_MORE_DATA