Added Cache class

Added generic Cache class that can be used for holding BTreeNode objects
Updated cache, better method names
Updated Cache and BTree

Cache contains more useful methods. Added in separate constructor for
cache implementation within BTree. Updated BTree close method
More Cache Implementation

added in cache checking for diskwrite method and close method, still
need to do diskread method
May have finished Cache

I cannot test it as it seems to have errors with normal reading and
writing to files, but cache is implemented into read and write methods
as needed.
Working bTree
Merged with Brian-Files