Implement sorted array Indexer

[0xnullifier]

The Idea of Sorted Array Indexer is to keep a simple list of Keys by Some compare function for example:

type ArrayIndex struct {
    sync.RWMutex
    keys []string
    compareFunc func compare(string keyA, string keyB) (string first, string second)
} 

You have to implement the Indexer interface for ArrayIndex . The following function:
Insert: adds a new key while maintaining sort order try doing this in O(n)
Initialize: Simple function to initalize the keys capacity
Delete: Do deletion in O(n)
Keys: Implement range queries do it in most.