Proposal for common 802.15.4 radio driver API definition.
shell: strings in shell_command_t are const
shell: Comment internal members, too

Closes #979.
Merge pull request #1065 from Kijewski/issue-979-2

shell: Comment internal members, too
Merge pull request #925 from rousselk/radio-driver-api-proposal

Proposal for common 802.15.4 radio driver API definition.
tests: added missing chronos to blacklist
Merge pull request #1063 from Kijewski/shell_command_t-fix-const

shell: strings in shell_command_t are const
Merge pull request #1066 from mehlis/test-bloom-bytes-followup

tests: added missing chronos to blacklist
test: thread: blacklist boards
Merge pull request #1062 from mehlis/test-thread-blacklist

test: thread: blacklist boards
make: remove clutter

Remove some outdated example code, and simplify output folder creation.
make: parallelize creation of board and base code
 make: add `BOARD_INSUFFICIENT_RAM` blacklisting

Currently most blacklistings for examples and tests are done because the
board provides too little RAM or ROM. Besides of the actual linking all
the compiling should nevertheless work just fine.

This PR adds the variable `BOARD_INSUFFICIENT_RAM` to tell the
`buildtest` to compile the code for a board, but omit the linking step.
Use `BOARD_INSUFFICIENT_RAM` in examples and tests
[SQUASH ME] add BOARD_INSUFFICIENT_RAM for test_posix_semaphore
[SQUASH ME] fixup test_bloom
[SQUASH ME] fixup #1062