v1.0.0-rc1

Rewrite to adopt ITCSS principles

Main changes:

• Re-structured cactus based on ITCSS
• Added linting
• Added automated tests
• Recategorised reverse group utility to modifier due to lack of reuse

Breaking changes

• .cactus__w, .cactus__g and .cactus__u classes prefixed to specify type -> .o-cactus__w, .o-cactus__g and .o-cactus__u.
• .o-cactus__greverse utility class -> .cactus__g--reverse
• Run npm run test to run automated tests
• Run npm run lint to run Scss linter