Add default travis configuration
Add travis shield to README

* presumably s/jefferis/hadley/ will be necessary
Merge pull request #3 from jefferis/master

Prepare for CRAN release
switch travis build shield to hadley's repo
Merge pull request #4 from jefferis/feature/travisci

Feature/travisci: add travis integration
Docs: <appname> -> <AppName> to avoid confusion

See ActiveState/appdirs@d6e084c104c702aabcad1a914fb9ec64bf41b8fc

We were not messing with appname, actually, which is good,
only the docs was "incorrect".
Docs: comment on appauthor -> appname fallback

ActiveState/appdirs@0826614d35be125f4637d01a5b1c5b628cb43fc2
The fallback was already in place.
Only use version if appname is not NULL

ActiveState/appdirs@71d586aef3d82ba4752bbdc8d3f241a5b751f73c