Version 0.4.0

Version 0.4.0

Changelog:

- NMEA
  - added class 'waypoint'.
  - added query functions for manufacturer information.
  - type for padding bits of the payload changed to uint32_t.
  - cleanup of public API of sentences.
  - constructing sentence objects differently, gains about 10% performance.
  - minor refactoring of checksum rendering, also faster.
  - preformance improvements in string splitting.
  - added benchmarks for some NMEA sentences, testing nmea::make_sentence

- AIS:
  - type for padding bits of the payload changed to uint32_t.
  - added benchmarking of AIS message decoding.

- Doc:
  - added GCC-6 and Clang-3.8 as supported/tested compilers.
  - exclude the namespace 'detail' from generated documentation.

- Build:
  - IO is now optional, use flag 'ENABLE_IO'.
  - minor cleanup for warning hell.
  - minor warnings cleanup

- Dev:
  - added Clang-3.8 debug build
  - added GCC-6 debug build
  - disabled travis-ci clang builds, llvm.org/apt is out of order at the moment.