STAT table validation

[robmck-ms]

We're starting to see a lot of incorrectly formed STAT tables. It would be great if Font Validator supported STAT tables.

One test case that's not entirely obvious from the spec: there can be only one AxisValueTable for a given coordinate on a given axis.

[HinTak]

Do you have a collection of such broken files? Wouse be useful if you could share those (if necessary, privately).