Enhanced at-tree and att-tree

[valaises]

Changelist:

At Tree

• restored symbols functionality
• added option parameter --ast
• improved parsing (only line with command is parsed now!)
• using plain_text role (supported by an alpha branch of chat-js)

Examples of usage:

or with specifying a dir

Note: --ast could be either before or after the path or absent

Att Tree

• added a new parameter: use_ast