Added a corpus reader for reading in either a single file of documents (one per line) or a folder of documents (one per file).
Added a python class for reading in metadata associated with a corpus.
Fixed symlink for welcome app.
Finished implementing all of CorpusReader, MetaReader, and SentenceReader.
Updated StreamingSentenceSplitter to flush output.
Updated import_corpus and corpus module to match the new corpus formats.
Updated demo to use the new import_corpus