Precaching feature for reCAPTCHA 2

Every time you solve a regular recaptcha for some domain this feature (if enabled) starts to solve another K recaptcha tasks for this domain in a background.
So when you request another recaptcha — it will be already in process of solving or even solved which will dramatically decrease a medium working time.
Especially effective for equally periodic requests for the same domain.

Attention!!! This option will increase spending since some of the so called precached tasks will be expired when you stop to request more recaptchas (Google set a 2 min lifetime for every solved recaptcha).
Our main goal now is to find a balance between an extra money waste and a solving interval.
We really appreciate any feedback about this feature usage. Together we'll make our plug-in great again!

It can be set up by changing a K-number (precachedSolutionsCountK) which determines how much of spare (not taken by any other process) precached solutions should be available for usage anytime.
To be more precise you can set a min-max interval within which this number should be.

The more frequent you need to solve recaptcha the more this number should be. The better min-max values can be found experimentally.
For typical usage we recommend the following values: min = 2 and max = 4.
Automatic algorithm will optimize the K-number in the Min Max gap you've chosen for a better performance and a less spending.
This K-number is different for every domain and calculated independently.