inaccurate minimap line length with proportional font

[ghost]

The minimap shows all characters with the same width, even if the user has selected a proportional font. It’d be more accurate if the size of the blocks in the minimap were reflected by the character sizes in the editor.

For example, if I enter the following lines in my editor:

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
llllllllllllllllllllllllllllllllllllllllllllllllll

The bottom line is clearly smaller, but the minimap shows them with the same size.

[ghost]

By the way, since I don’t think anyone else would actually bother about this issue, I decided to work on it myself: #656.