Implement tools for finding operations in a specification file

[Manfred]

When projects publish their endpoint specs in an extremely large file you may want to find a very specific endpoint without having to scan it in a text editor or your terminal.

# Find all endpoints that have `author' in their operation id, description, or summary
reynard search author

It may be useful to keep a cached version of the sources and use conditional requests to speed up interaction. We should also fall back on a cached versions when an HTTP request fails with a server error.