Add DB file generation task

[sho-h]

I want to add gems/*.yml more easily. As a trial, I add rake tasks to fetch information from RSS and create yaml file in ruby/rails.

$ rake db:update         # check and create all
$ rake db:update:ruby # check and create only ruby file
$ rake db:update:...

This commit still have several bugs and many TODO. For example, date format is invalid. And still need human checking. But first YAML file creation task is easier if merged.

[postmodern]

I like the idea of being programmatically alerted based on RSS feeds, which could become a separate library/framework onto itself. Have you looked into IFTTT by chance? It allows you to setup conditional rules that watch feeds, searches, etc.