separate similar but different properties for saucelabs/browserstack
updated readme, fix bug in optional browser version code, and add test
link the readme to the config code
fix up relative readme link to config class
minor updates to explain how to fill in the platform
Merge pull request #27 from guardian/config-saucelabs-tidyup

Minor config fixes - *some browserstack property names changed*
Merge branch 'master' into s3-changelog