pthread: pthread_barrier should call yield
tests: clean up test_pthread_barrier Makefile
core: add `thread_get()`

Remove PID check duplication in `thread_getstatus()` and
`thread_getname()`.
board/stm32f3discover: fixed LED macros
cpu/stm32f3: let LD3 blink on hardFault
Merge pull request #1576 from haukepetersen/fix_stm32f0_leds

cpu/board: fixes to stm32f0(discovery)
drivers: improved the low-level GPIO driver IF

- removed UNDEFINED value from device enum
- changed most functions to void return value
- add parameter for interrupt callback
cpus: adjusted uart implementations for changed IF

- adjusted stm32f0
- adjusted stm32f3
- adjusted stm32f4
- adjusted sam3x8e
- adjusted nrf51822
tests/periph_gpio: added test cases for GPIO driver
Merge pull request #1484 from haukepetersen/fix_drivers_gpioif

drivers: improved IF for low-level GPIO driver
Merge pull request #1562 from Kijewski/the-first-two-commits-of-the-branch-issue-198

posix: minor pthread_barrier clean up
pyterm: fix exit behavior if twisted is not available
Merge pull request #1582 from N8Fear/fix_pyterm_twisted

pyterm: fix exit behavior if twisted is not available
Merge pull request #1580 from Kijewski/thread_get

core: add `thread_get()`
all over the place: use sched_active_pid

In many places we needlessly use `sched_active_thread->pid` whilst we
already have `sched_active_pid` with the same value, and one less
indirection.

`thread_getpid()` is made `static inline` so that there is no penalty in
using this function over accessing `sched_active_pid` directly.
core: SCHED_PRIO_LEVELS==16 for every board

Closes #1399.

> Using a different value for SCHED_PRIO_LEVELS for 16 and 32 bit
platforms hurts portability, one thing that we heavily advertise about
RIOT. if you want to write a portable application, then you have to
assume the lower value.

This PR defaults `SCHED_PRIO_LEVELS` to 16 for every board.
make: added CPU_MODEL & TERMFLAGS to Makefile.vars

- added CPU_MODEL variable
- added TERMFLAGS variable
- fixed a little style (dots on the end of comments)
Merge pull request #1591 from haukepetersen/fix_make_vars

make: added CPU_MODEL & TERMFLAGS to Makefile.vars
board/pca10000: added make targets

- added `reset` target
- added `debug` target
- added `debug-server` target
- adjusted `flash` target
Merge pull request #1590 from haukepetersen/fix_nrf_maketargets

board/pca10000: added make targets