Support readview

[DifferentialOrange]

readview API was introduced in Tarantool EE 2.11: https://github.com/tarantool/tarantool-ee/issues/140 . It is a way to get a consistent view of a space data.

Product team API proposal is as follows:

local readview = crud.readview{option = optvalue, ...}

local lst = readview:select(...)

for _, tuple in readview:pairs(...) do
...
end

readview:close()

Options:

• lazy -- boolean (create readview on each instance on crud.readview or only when instance has been reached),
• ttl of a readview.