Histogram() can only process CSV files

[dnut]

Improve compatibility for other table types.

[dnut]

Possible solution: Create Table() class to act as interface between histogram and table.

class Table():
	def __init__(self, table_format, location, output):
		""" Choose format (eg. csv), location (eg. file), output (dict or list) """
		if location and format:
			self.head()

	def head(self):
		""" Get first row from table """

	def row(self):
		""" Generator exposing successive rows as lists or dicts """

	def csv(self):
		""" Format specific methods used by row() """
		if dict: dictreader
		if list: reader