Store function definitions in the cache.
Add some comments to explain the cache fill process.
Invalidate the old definitions cache when reparsing.
Change the list of RPC functions for our service.

We had a bunch of "sample" functions for our protocol. This commit removes
everything except what we actually use right now.
Add the cache lookup function.
Wire cache lookup to the find_definition RPC function.
Remove useless logger calls.
Implement a client definition lookup.