Modularize filters

[jofftiquez]

Make filters exportable separately so that it can be tree shaking friendly.

Sample:

// import all filters and directive
import { VueMorphling } from 'vue-morphling';

Vue.use(VueMorphling);

// use selected filters and/or directives
import { morphUpperCase, morphDate, vMorphHighligh } from 'vue-morphling';

Vue.use(morphUpperCase);
Vue.use(morphDate);
Vue.use(vMorphHighligh);