Use DEFAULT_ASSISTANT_ROLE everywhere instead of 'crt'
Fix title underline in command reference
Introduce task assistants
Allow deep formating command without evaluating expressions
Allow adding arbitrary content to .devassistant from yaml assistants, fixes #21
Tidy up DotDevassistantCommandRunner, adapt dependencies installation to current style (don't go through all assistants as we did prior to 0.8.0)