Improved Stage Title Cards

[StarWitch]

Similar in idea/concept to #263, except for stages. We currently have them but they're easy to miss and not terribly pretty-looking. Mainline Touhou games have had fancy-looking ones since at least EoSD, and so do many fangames. It'd probably go a long way to helping the player understand where they are in the story as well. It'd be a call available to stage timelines to be called whenever it's convenient.

(example from Ten Desires)

[Akaricchi]

This should be already easy to implement with the stagetext API, at least the text part of it. Just remove the automatic generic "title cards" from stage.c (the display_stage_title function) and insert manual stagetext_add calls into the stages. The real work here is designing the title cards (i.e. writing the text and choosing a layout), which I'll leave up to you :)

After we have that done, we can add a similar mechanism for displaying overlay images/animations if we ever want to make them fancier, but I think for now just text is enough.