Merge pull request #1 from korpling/develop

update changes from korpling for September
added meta options for textexporter
added public appendMetaData() method to the GeneralTextExporter class, which is a super class to Grid and TextExporter. The method is called from subclasses Grid, Text, and SimpleText Exporters to append metadata to the exported file. The original private appendMetaData() method implemented in the GridExporter class is removed from that class.
added meta:: double colon
Merge pull request #360 from zangsir/issue306-metakeys-for-textexporter

closing #306 (metakeys for textexporter)