Add monoid for arrays.
Add monoid for arrays.

rklaehn/spire,tixxit/spire,non/spire,kevinmeredith/spire,AlecZorab/spire,JackSullivan/spire,woparry/spire,JackSullivan/spire,tixxit/spire,siddhartha-gadgil/spire,adampingel/spire,rklaehn/spire,guersam/spire,siddhartha-gadgil/spire,guersam/spire,non/spire,woparry/spire,AlecZorab/spire,kevinmeredith/spire,codeaudit/spire,codeaudit/spire,adampingel/spire