Add readme for the hello-world example

Closes #1070.
added NORETURNs to functions that should not return
and added `UNREACHABLE();` to hint the compiler unreachable lines

added right signature for first parameter of `thread_stack_init()`
added `UNREACHABLE();` macro to `cpu/lpc1768/atom.c` and `cpu/msp430-common/cpu.c`
Merge pull request #1072 from Kijewski/issue-1070

Add readme for the hello-world example
shell:ps: SCHEDSTATISTICS cols only if needed
make/native: remove -gc flag

Yields warning on OSX.
Uncertain why it was there in the first place.

Fixes #1125
Merge pull request #1126 from LudwigOrtmann/issue-1125

make/native: remove -gc flag
Introduced a cleaned-up cpu/core interface

- Included a collection of cpu-dependent headers in core/include/arch
- Extracted all interfaces that need to be implemented for a cpu
- Created a mapping between those interfaces and the old ones
- added flag for disabling arch interface
- added missing state to lpm_arch interface
- added arch interface for reboot
- fixed newline issues that were pointed out
- documentation fixes to cpu-core interface
Merge pull request #507 from haukepetersen/core_cpu_interface

Introduced a cleaned-up cpu/core interface
Merge pull request #1122 from Kijewski/ps-SCHEDSTATISTICS

shell:ps: SCHEDSTATISTICS cols only if needed
Remove superflous apt-get update from .travis.yml
Add unittests to .travis.yml
typo fix
removed unreachable code
msba2: add pseudoterm license
Merge pull request #1134 from kaspar030/pseudoterm_license

msba2: add pseudoterm license
Merge pull request #1132 from jan-schreib/master

Removed unreachable code and fixed a typo.
Exclude *.c files from make doc
examples/default: add README.md

Fixes #1068
Merge pull request #1071 from LudwigOrtmann/issue_1068

examples/default: add README.md
make/msba2-common: allow TERMPROG override