Merge tag 'stevedore-0.8.0-beta.4' into develop

stevedore-0.8.0-beta.4
Updated version for next release cycle
Support using multimethods as script functions
Allow vector values in map-to-arg-string

In pallet.stevedore/map-to-arg-string, make keys with vector values
result in having the switch repeated for each value in the vector.
Updated project.clj, release notes and readme for 0.8.0-beta.5
Merge branch 'release/0.8.0-beta.5'