Provide a "smarter" document formatter

[dklilley]

Is your feature request related to a problem? Please describe.
Current document formatting only modifies preceding and trailing whitespace on lines. It would be great if it could handle more advanced formatting, like adjusting whitespace within a line (e.g. a = 4+ 5 formatted to a = 4 + 5).

[gregdvd]

Related to this, is there a reason why the formatter adds spaces in empty lines? Trailing spaces are usually discouraged (at least in my experience), and raise warnings with, e.g., git diff --check.

In this example I've replaced the trailing spaces added by the formatter with the · sign, to make them visible.

j = 0;
l = 0;
for i = 0:10
    j = j + 1;
····
    l = l + 2;
end