Fix #34; allow adding errors at runtime
Write tests for runtime errors
Add one more test to check the result
Fix #56; prevent manually setting the result
Merge branch 'execution-errors' into v0.5.0
Rename "@result" to "@_interaction_result"

This makes the possibility of a collision much lower.
Update changelog
Version bump to 0.5.0
Add a more visible link to the documentation
Point the homepage to GitHub Pages

Also add a link to it from the readme so that people can navigate back
from RubyDoc.info.
Merge branch 'master' into remove-default-from-hashes