Creating abstract Sheet interface

Removing [read|write]_book and guess_[read|write]. Transposition still happens at this level.
Removed ExcelInterface from xlmp.py
Simplified Mapping functions

Adds dependencies to ISheet
wrapper functions use SheetIO as I want them to.
Created ISheetIO abstract class derivates

This is something that needs reviewed.  SheetIO is both the interface and factory for the class.
pass -> raise
_
Created CsvSheet class