Custom identifiers for variable substitution

This release introduces custom identifiers for variable substitutions. The identifiers to be used must be specified when the plugin is initialized. Start and end tags should be specified. Please be aware, that a regular expression is used to find the tags and respective escape characters should be used.

// initialize the vuexi18nPlugin
Vue.use(vuexI18n.plugin, store, 'i18n', ['{{', '}}']);