Support for `StreamReadConstraints.maxNameLength` and `maxStringLength` for YAML parsing

[cowtowncoder]

(note: cleaved off of #430).

So: while some StreamReadConstraints constraints are enforced (like Max nesting depth, max number length), two constraints are not yet but should be supported:

1. Maximum name length
2. Maximum String value length

and it should be relatively easy to add these.