Arrays of Arrays of Tables

[ear7h]

Trying to parse the following TOML:

x = [ [ {a = 1} ] ]

Results in:

  |
1 | x = [ [ {a = 1} ] ]
  |         ^
unexpected '{'
expecting ']', array, bool, datetime, double, integer, or text

Looking at the various types it seems like this would would be nontrivial to support, since the Value type cannot have tables. This might be something to consider wrt #264 and #373