Date recogniser returns "not resolved" (documentation)

[brazierdavid]

Documentation issue only I think: it appears that "not resolved" can be returned as a value in many cases, particularly for dates (see https://github.com/microsoft/Recognizers-Text/search?p=2&q=not+resolved). Normally, the value is expected to be in yyyy-MM-dd format etc, so callers should check for "not resolved"? Are there any other special values callers should check for?

[hazemelh]

@fxs130430 To look into this further