update RStudio project
Travis-CI configuration changes

- enable multi-OS builds as per http://blog.travis-ci.com/2014-05-13-multi-os-feature-available/
- dump various logs
- treat warnings as errors
docs: caveats section notes race conditions

* also move details re CRAN policies out of description and into a new
  caveats section lower down.
Merge pull request #15 from jefferis/feature/package-docs-caveats

docs: caveats section notes race conditions
Merge pull request #7 from krlmlr/setup

Setup