msp430: fix missing members in `struct tm`

Closes #1150.
native: initialize maybe uninitialized variable

fixes #1118
Implement core unittests
unittests: Move tests-core into subdirectoy
native: refactor one debug/errx use in irq_cpu.c
native/tramp.S: use ret instead of manual return
Merge pull request #1179 from LudwigOrtmann/native_minifix

Native minifix
core/doc: complete hwtimer.h and hwtimer_arch.h
core/doc: complete queue.h
core/doc: complete io.h
Merge pull request #1041 from LudwigOrtmann/issue_951

Fix doxygen comments for hwtimer.h, queue.h and io.h
Merge pull request #1177 from LudwigOrtmann/issue-1118

native: initialize maybe uninitialized variable
Merge pull request #1154 from Kijewski/issue-1150

msp430: fix missing members in `struct tm`
Merge pull request #961 from authmillenon/core-unittests

unittests: Unittests for core module data strutures
license checker WIP