Split constraints into smaller functions (#367)

* Start splitting up large functions

* Abstract out flip x and flp y together

* Update constraint.js

* Fix setting left/top

* Add some docs, start some tests

* Add tests for _calculateOOBAndPinnedTop

* Start _flipYTogether tests

* Update constraint.spec.js

* Add flip X tests

Author: RobbieTheWagner

babel.config.js

@@ -20,6 +20,7 @@ module.exports = function(api) {
           ]
         ],
         plugins: [
+          'babel-plugin-rewire',
           'transform-es2015-modules-commonjs'
         ]
       }

package.json

@@ -40,6 +40,7 @@
     "@testing-library/jest-dom": "^4.1.0",
     "autoprefixer": "^9.7.0",
     "babel-jest": "^24.9.0",
+    "babel-plugin-rewire": "^1.2.0",
     "babel-plugin-transform-es2015-modules-commonjs": "^6.26.2",
     "chai": "^4.2.0",
     "cssnano": "^4.1.10",