Fix crash when using --trace 10 or above

uint8_t is typedef'd to char, thus boost::lexical_cast treats it
as such instead of a number.
Ignore vim swap files
[ci skip]
[test] Use --args-only option in DocTests.py

instead of --init-file /dev/null
[travis] Shorten Travis CI run times

by adding --jobs to utilize multiple cores and using boost ppa packages
instead of downloading the source and building boost from scratch.

This effectively cuts the time for a Travis CI run in half.
Merge pull request #352 from afh/pull/travis

[travis] Shorten Travis CI run times
Merge pull request #349 from afh/pull/DocTests

[test] Use --args-only option in DocTests.py
Merge pull request #346 from afh/pull/trace_level

Fix crash when using --trace 10 or above
Merge pull request #347 from afh/pull/gitignore

Ignore vim swap files