Add PageLoaders

Examples:
ParsoidPageLoader = require( './pageloader/ParsoidPageLoader' ).ParsoidPageLoader
l = new ParsoidPageLoader( 'http://parsoid.wmflabs.org', 'enwiki' );
promise = l.load( 'Food' )
promise.then( function ( x ) { console.log( x ); } );
promise.done();

MediaWikiApiPageLoader = require( './pageloader/MediaWikiApiPageLoader' ).MediaWikiApiPageLoader
l = new MediaWikiApiPageLoader( 'http://en.wikipedia.org/w/api.php' );
promise = l.load( 'Food' )
promise.then( function ( x ) { console.log( x ); } );
promise.done();

Change-Id: Iddc35275dbf71ecf549fb834528722242800ce96
Correction in dummy sentence segmenter

Split using period+space instead of period.

Change-Id: I2eabba15bd616f0777ded4332fe8d177bbfeb112