csvstat: Add support for --no-inference

[jpmckinney]

Use case:

I have strings of the form "1-1-19" and "1-1-20". I want e.g. counts of those as unique strings. They are interpreted as dates which adds massive confusion. I'd love to have both implicit inference for numbers, and no fancy guessing of "implicit dates" since the latter is so wide-ranging and convoluted in the international public mind.

From #935 (comment)

[jpmckinney]

Fixed!

Previously, to reproduce:

$ printf "a\n1-1-19\n1-1-20" | csvstat
  1. "a"

	Type of data:          Date
	Contains null values:  False
	Non-null values:       2
	Unique values:         2
	Smallest value:        2019-01-01
	Largest value:         2020-01-01
	Most common values:    2019-01-01 (1x)
	                       2020-01-01 (1x)

Row count: 2