[3pt] Describe new digest module function for xxHash32/64

Describe the new digest module function for xxHash32/64

Product: Tarantool
Since: 2.9.1
Audience/target: Tarantool users
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_lua/digest/
SME: @olegrok
Peer reviewer: @

Details

-- Examples below demonstrate xxHash32.
-- xxHash64 has exactly the same interface

-- Calculate the 32-bits hash (default seed is 0).
digest.xxhash32(string[, seed])

-- Streaming
-- Start a new hash by initializing state with a seed.
-- If no value provided, 0 is used as default.
xxhash = digest.xxhash32.new([seed])
-- Also it's possible to specify seed manually. If no value
-- provided a value initially passed to "new" is used.
-- Here and below "seed" expected to be unsigned
-- number. Function returns nothing.
xxhash:clear([seed])
-- Feed the hash state by calling "update" as many times as
-- necessary. Function returns nothing.
xxhash:update('string')
-- Produce a hash value.
xxhash:result()

• Related development issues and/or commits: https://github.com/tarantool/tarantool/commit/f998ea39e96d93113823d92727a1faf9860c8ea6

Definition of done

• The new digest module function for xxHash32/64 is described.

Start at the root digest documentation: https://www.tarantool.io/en/doc/latest/reference/reference_lua/digest/ and inspect the related commit f998ea39e96d93113823d92727a1faf9860c8ea6. Document the xxHash32 and xxHash64 one-shot and streaming interfaces, including seed behavior, and mark the issue done when both functions are described for Tarantool users.