make: comprehensive list of the boards' filesizes
make: add maketarget to to show the biggest obj files
make: show diffence in buildsizes for two folders
Proposal for common 802.15.4 radio driver API definition.
shell: strings in shell_command_t are const
Add basic travis-ci integration

This PR adds the basic integration for [Travis CI][tci].

The config file `.travis.yml` tells the server to setup the basic build
system, and run `compile_test.py`. If not all  examples and tests could be
built, then the Travis CI integration adds a warning to "merge" button on
the bottom of the Github page.

Of course this integration makes little sense until #1049 is resolved,
because new bugs and old bugs cannot be told apart. Also (of course)
only because everything still builds, a PR still can intruduce a
multitude of runtime errors.

This integrations is meant to work additionally to our Jenkings. Users
can activate the test in their own RIOT forks to run the test before
opening a PR to master.

  [tci]: https://travis-ci.org/
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
Merge pull request #1055 from Kijewski/travis-ci

Add basic travis-ci integration
drivers: fix includes in rtc.h for MSP430

The comment and the actual guard in `rtc.h` did not match.
If (as in "implication") the MCU is an MSP, then `sys/time.h` must be
included, to have `time_t`, `struct timeval`, …

Including the header file in any case should be safe, so I dropped the
guard altogether.
Merge pull request #1033 from Kijewski/buildsizes

make: comprehensive list of the boards' filesizes
add pthread condition variable implementation
Merge pull request #771 from BytesGalore/add_CV_module

pthread: Add condition variable module
added else branch in `pthread_exit()` to avoid calling explicit `return;`
however, this won't help to completely eliminate the warning on returning from a `noreturn` function