Add `csvz-meta-meta`

[secretGeek]

A file can have

_meta/meta.csv

describing which of the standards you claim conformance with. e.g.

fragment	conformance	notes
csvz-0	strict	this csvz file claims strict adherence with csv-0
csvz-meta-tables	strict	yes we have a _meta folder with a tables.csv file in it

...If they only claimed those two rules were followed then it would be up to the consumer to read the files and determine for themselves how to make sense of them.)

(suggestion: tools could generate this, or at least a draft f this, and tools can use this for configuring their own expectactions.

[secretGeek]

(This is inspired by @items in issue #14