Don't bother nilling out _contents
All ivars start out life as nil. Setting to nil yourself is a waste of time
Make _entries a non-mutable NSArray
There's never an occasion where the array is mutated in any way other than rebuilding it, so might as well use NSArray. Happily this also ensures callers of -entries will never get passed back out an array that might mutate underneath them
Merge pull request #20 from mikeabdullah/ivars

Improve treatment of instance variables