Add vx_peek
Use vx_peek
Use letter as column name
Reorder lines
Add detect_data_rows
Use detect_data_rows
Add detect_sheet_header
Add under_name
Use detect_sheet_header
Use check_for_constant_string
Use check_for_constant_string
Use check_for_constant_string
Use check_for_constant_string
Add period_start
Add period_end
Use cell_value
Use self.book
Use self.xlrd
Use self.xlrd
Add vx_date