Use formatter for searchstring

[bmschmidt]

Manually constructing a searchstring for every document is silly, because:

1. They're really formulaic, and this takes up space
2. Sometimes I want to use information that won't be on hand until later data joins are accomplished.

So it should be possible to create a bookworm with no search string, and add it later.

Here's a gist with code for making the ChronAm searchstrings after the fact; a later edition will be even better, since it will be able to give the paper titles (not part of the raw metadata bundle, which only gives unreadable LOC identifiers).

[tpmccallum]

I really like this idea, I have not added search string to the documents in the hope that the user can receive a search string with perhaps a title and url in context to the word[s] they searched for.