feat(dsl): exposes DSL for end users to create their own layout syntaxes

[runspired]

Fixes

• fix CSS compilation
• fix layout lookup for non-prefixed pods

Features

• configurable DSL via config/flexi.js
• offsets can now be used within breakpoint attrs

Hooks
These only modify the class names generated in your html, not your CSS (css versions coming soon)

• generateGridClass: function(breakpoint, colNumber, columnPrefix, totalColumns) {}
• generateResponderClass: function(breakpoint, responder) {}
• generateAttributeClass: function(property, value) {}
• generateOffsetClass: function(breakpoint, colNumber, columnPrefix, totalColumns) {}

syntax

• elements: [] // element tags to look for attributes on
• responders: [] // responsive attributes usable within breakpoint attrs
• attributes: [] // attributes usable directly on elements

elements and responders should both be arrays of strings.
attributes should be an array containing strings for attributes based on "presence" and objects for attributes with values. Objects should have name and values properties.

example:

attributes: [{ name: 'justify', values: ["start", "end", "center", "between", "around"] }]