Improve lifetime of the eval cache

Per discussion with @LouisLaf and @pleath , there is room to improve the eval cache so it will cleanup before a navigation takes place to conserve memory. Please evaluate an LRU cache using the following possible inputs. It is possible other inputs make more sense so please consider this a list of ideas rather than a requirement.
- Time since used
- Size of data
- Available memory
- Possibly a toggle to shrink further when given a signal from host