Allow Build on Windows

Builds on windows were failing due to specs relying on *Nix line endings
/ file separators.
added manifest to core.gradle to allow spock core to work in OSGi land
mention 1.0-groovy-2.3-SNAPSHOT in readme
added another test for @Stepwise
added appveyor build definition
switch appveyour build to jdk8 (jdk7 didn't install correctly)
configure appveyour build
Merge branch 'pr/38' into groovy-1.8
configure appveyour build
Merge branch 'pr/40' into groovy-1.8
slightly updated and reformatted osgi bundle information
Merge branch 'groovy-1.8' into groovy-1.9