sys/transceiver: make transceiver_pid volatile

- because it is
SQUASHME: clean out extern kernel_pid_t transceiver_pid redefinitions
buildtest: retry failed builds once

On Travis CI often builds fail spuriously.

This PR lets `make buildtest` retry the build once.
cpu/cortex-mX_common: bugfix to arch_stack_init

- fixed cortex-[m0|m3|m4]
doc: fix flashrom doxygen
boards/cpu: fix some warnings
Merge pull request #1547 from haukepetersen/fix_cortex_threadarch

cpu/cortex-mX_common: bugfix to arch_stack_init
"tests": print tcb_t size

The "test" should aid #303.
Merge pull request #1525 from LudwigOrtmann/morning-cleanup

doc, boards/cpu: cleanup
Merge pull request #1535 from LudwigOrtmann/transceiver_volatile

sys/transceiver: make transceiver_pid volatile
cbor: CBOR implementation for RIOT-OS

This is a malloc-free implementation of the Concise Binary Object
Representation (CBOR) data format for the RIOT-OS.

This implementation mostly stand-alone, and it should be pretty easy to
port to other platforms. We're only using the C STL and some custom
network-related functionaliy which could be easily replaced by depending
on arpa/inet.h.

The CBOR API is straight-forward to use and provides encoding/decoding
functionality for all major C types, such as:
- int
- uint64_t
- int64_t
- float
- double
- char*
- struct tm
- time_t

It is possible to conditionally compile this module via CFLAGS:
- CBOR_NO_SEMANTIC_TAGGING: All semantic-tagging features removed
- CBOR_NO_CTIME: All ctime related features removed
- CBOR_NO_FLOAT: All floating-point related features removed
- CBOR_NO_PRINT: All features depending on printf removed
Merge pull request #1548 from Kijewski/print_size_tcb

"tests": print tcb_t size
Merge pull request #1415 from krf/cbor

cbor: CBOR implementation for RIOT-OS (SWP)
make: added targets 'debug-server' and 'reset'

- added targets to Makefile.include
- added DEBUGSERVER and RESET vars to Makefile.vars
- added output of those to Makefile.buildtests
boards/stm32fXdiscovery: added debug-server target

added "make debug-server" target for
- stm32f0discovery
- stm32f3discovery
- stm32f4discovery
make: msb-430 boards: added debug and debugserver targets
Merge pull request #1542 from haukepetersen/add_make_moretargets

make: added targets 'debug-server' and 'reset'
driver_periph: minor documentation fix
x86: disable `--gc-sections` for Travis' sake

I could not reproduce the problem at home, but on Travis CI after
merging #1415 tests/unittest failed to execute for qemu-i386.

There is a crash early in the initialization, caused by a #PF. The
execution hangs afterwards (`cli; 0: hlt; jmp 1b`), and Travis kills
the execution after 10 minutes.
Merge pull request #1551 from authmillenon/fix-periph-doc

driver_periph: minor documentation fix