Big & breaking updates!

This is a little bit too soon for what I've had planned, but I just want to check this off my list.

New

• Added {( expression )} tag (#66)
  You can execute, evaluate, and then insert any valid GDScript expression, with any scopes registered, using this new expression tag.

  Dia:
    "Your operating system is {( OS.get_name() )}.
    It is currently {( Time.get_time_string_from_system(false) )}.
    And the Godot version of this project is Godot {( Engine.get_version_info()["Major"] )}"

  This tag, and scoped variables should also works inside actor label.
• [img] BBCode tag is now fully supported (#41)
• Add [f] alias for BBCode tag [font] (efbef3b)
• Add syntactic sugar for [img] BBCode tag: [img h=20 w=20 res://icon.png]. (#84)
• Class references (properties, methods, signals) are now available in the online documentation.

Changes

• Dialogue tags are now case sensitive. (1279d18)
  Previously, built-in dialogue tags, like {delay}, are the same as {DELAY}, or {dELaY}. Now, all dialogue tags strictly uses lowercase.
• TheatreStage: scope_nodes are now Dictionary[String, Node] instead of Array[Node]. (9f54a06)
  Where you define the scope ID as the key, rather than setting the node's name as the scope ID.
• DialogueLabel: The parameter rendered_text is now removed from the signal text_rendered. (#95)
• DialogueLabel: Replace characters_draw_tick with chars_per_second unit. (#96)
• Improve online documentation.
• Various bug fixes and performance improvements.