This fixes our formatting for multiline selections with the toolbar. Before,

the formatting symbols would only be put at the beginning of the first line and

end of the last line, but now we put them at the beginning and end of each line

in the selection. This also fixes a bug for multiline selections that had

a smaller line length for the first line than the rest of the lines. Applying

formatting to these types of selections would lead to an infinite loop.

Tested bold, italic, strikethrough and code formatting with various single

line and multiline, selections and no selections.