v0.0.18

Added

• Add reference for commands in ref
• Add completion for commands in ref
• Add completion for env variables in cmd scripts from global and command env

Internal

• Refactor completions in a way to use LetsPsiUtils
• Drop Config, refactor into `ConfigParser
• Drop LetsCompletionHelper
• Introduce YamlContextType enum instead of boolean functions for determining context type (position type)