Write ngram files to current directory.

Also added notes on bulk upload of data to GAE.
WIP for allowing clickthrough to posts.

Modified mfngram.py so the temporary joined post data file is now kept
as posts.tsv.
Renamed bulkloader_custom.yaml to bulkloader_ngramcount.yaml.
Added bulkloader_post.yaml.
Added a /post URL that requests JSON-encoded post info for multiple
post IDs.
User can select a year and see posts from that year.

Changed post titles from StringProperty to TextProperty: There were
posts with titles longer than the 500 character limit for
StringProperty.