Update webpack and dependencies and remove gulp

Update dependencies and devDependencies.
Remove gulp dependency completely and just use webpack and npm for running builds.
Update to Webpack 2 and modify plugins and loaders accordingly
Update package.json to include semver build scripts so we can easily bump the version.
Update README documentation

Author: jfusco

.eslintignore

@@ -1,4 +1,4 @@
 /node_modules/
 /dist/
-/dist-components/
+/__mocks__/
 /__tests__/

README.md

@@ -204,7 +204,7 @@ $tag-input-border
 $tag-input-placeholder-color
 ```
 
-If you don't care to override variables and just want to override actual styles you may choose to import the minified compiled version of the css instead
+If you don't care to override variables and just want to override actual styles you may choose to import the compiled version of the css instead
 ```scss
 @import "node_modules/react-tagging-input/dist/styles.css";
 ```