Meta query date functions

[roborourke]

In some cases with a meta query you might want to build out a date query and use dynamic ranges, or make comparisons to date information for other purposes without necessarily casting values to date/time types. This is a little step in that direction that we've used in projects via a pre_get_posts filter, would be great to get your thoughts on the approach.

[ryanwelcher]

Overall, I love this idea!

I have a couple of thoughts that I'd love to get your input on:

1. The strings being passed are very developer focused will not mean anything to many (or even most) users of the plugin. Perhaps instead we can use more human readable strings?
2. The user will also have to know how the meta date is formatted in order to build the value out. There may be some need to expose this to them somehow. I imaged that ACF/SCF, Pods etc may handle that data differently - I have not checked to confirm this however.
3. It would be great to extend this same approach to the Post Date controls so perhaps this might be better done in the Query_Params_Generator class after the rest of the parameters are processed?

Great work and thanks for the PR!

[roborourke]

Yeah I wondered about the params generator but felt that had the UI and options already there for dynamic dates. I’ll look again to see what consolidation we can do. I’d gone for developer focused terms I think because the advanced meta queries felt like you need to know about data types and things already, but you’re right, they can be any strings so user friendly terms is a great shout.