Add `buildTag()` method to `Match` class

[gregjacobs]

When using the replaceFn, users should be able to call match.buildTag() to get an HtmlTag instance instead of autolinker.getTagBuilder().build( match )

Can also possibly remove the first argument from replaceFn() (currently the Autolinker instance) by passing the Match object as both arguments. The Match object should also have at least mostly the same public interface as Autolinker itself has for use in a replaceFn to maintain as much backward compatibility as possible. Ex:

replaceFn : function( match, sameMatchForBackCompat ) {
    match.getTagBuilder().build( match );  // for back compat with prev 1st arg: autolinker.getTagBuilder().build( match )
}