Modernize #pragma marks
Add variant of cache audit method that has a completion block.
We should be auditing in the background asynchronously. Oversight.
Add TJTree class.

Three operations:
1. Add string to tree
2. See if string is contained within C
3. Reset the tree

Note:
- Using @synchronized because I expect operations to this to happen on any thread
- Using C strings for performance reasons (not having to copy substrings. Could use -characterAtIndex: alternatively.)
- Using ivars rather than properties to avoid method calling overhead.
Added alternative method for auditing the cache.

Call +addAuditImageURLToPreserve: repeatedly (from any thread) to mark a URL to be preserved, then call +commitAuditCache to audit the cache asynchronously preserving the images you've marked.
Remove silly arbitrary cache limit.
Leverage NSMapTable for in-memory caching where available.
Update #pragma mark syntax