urlstore: cached url fetch as unix pipe

The command takes a stream of urls from stdin and outputs contents:
$ cat urls | urlstore.py fetch | process-the-output

When pointed to a JSON api, urlstore acts as a unix pipe to convert 
lines of url to the json output stream:

echo http://github.com/api/v2/json/repos/search/url+store \
	| python urlstore.py fetch \
	| json-cut repositories/[]/name
url_store
url-store
urlStore

The main usage is to avoid hitting a site with same url while 
investigating the api.  After the first invocation, the content 
is fetched from a local store, so you can rapidly iterate like you 
are grepping a local file.

API
Url that returns JSON can be converted to python data by store.data(url):

>>> from urlstore import Store
>>> store=Store()
    # convert url to data (assuming that the url returns json)
>>> for repo in store.data('http://github.com/api/v2/json/repos/search/url+store')['repositories']:
...     print repo['name']
...
url_store
url-store
urlStore