The patch add a generator which, when asked for an operation, logs a message and yields `nil`.

The patch add a function that takes a random mixture of a number generators and chooses between them uniformly.

The patch add a generator that produces concurrent atomic updates to a shared register.

Bump luacheck version to v1.2.0 [1]. 1. https://github.com/lunarmodules/luacheck/releases/tag/v1.2.0

Prepared statements improve performance by caching the execution plan for a query after the query optimizer has found the best plan. However, with simple queries (such as simple selects/inserts with no joins) prepared statements won't give a big improvement since the optimizer will quickly find the best plan. This commit enables using prepared statements in test examples and renames SQLite helpers.

list-append generator was broken, proposed commit fixes it and now an example from documentation works fine: > log = require('log') > tests = require('molly.tests') > for _it, v in tests.list_append_gen() do log.info(v()) end Fixes #3

- Fix executing of a `close` method due to early return - Add logging to client methods - Fix errors in test examples Fix #2