Mini-map feature

[1024jp]

A request from a user (see also: the issue #429.)

The Sublime Text style mini-map for navigation. To creating mini-map itself is actually not so hard, I suppose. Just create another text view and layout manager with an enough small font besides the main ones, and put them into a split view. However since this implementation must make the view structure more complex and deeper, we need to design it carefully. Furthermore, we also need to take care for the text-orientation switching.

Well, at the moment, I don't have a specific plan for this. Just for a note. May be later.

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Sublime Text のあれ。 まぁ、できないことはないけど、ややこしそうだからそのうちだなぁ、という感じ。