Several fixes:
- #223 fixes #199 Prevent empty line attributes in (junit) XML by @michaelbutler
- #228 fixes the build for php 7 by @michaelbutler
- #229 Update README.md with more information by @michaelbutler
- #225 fixes #164 and #146 Allows groups to be specified, event if test suites do not contain tests for them by @t11n
- #224 Fix temp dir inconsistency on os x by @elliotfehr
- #223 Add gitattributes file by @jdufresne