## feature/lua/log

* Implemented support of symbolic log levels representation in `log` module
  (gh-5882). Now it is possible to specify levels the same way as in
  `box.cfg{}` call. For example, instead of
  ``` Lua
  require('log').cfg{level = 6}
  ```
  one can use
  ``` Lua
  require('log').cfg{level = 'verbose'}
  ```
