Add readme for the hello-world example

Closes #1070.
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
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.
examples/default: add README.md

Fixes #1068