<line> overflows narrow card widths

[bszonye]

When printing cards narrower than about 5 cm, the graphic overflows onto a second line. Looks like the problem is the fixed width of this substitution:

    # <line>
    replace = "<center>{}</center>\n".format("&ndash;" * 22)
    text = re.sub(r"\<line\>", replace, text)

Instead of a fixed 22 en dashes, it should probably have a maximum width of 4 dashes times the text width in centimeters.

Alternately, the code for labels suggests that 4 cm is the minimum useful width for card text, so you could also change the output to a static 16 en dashes, which appears to be narrow enough for that width.

[bszonye]

I discovered that it's possible to determine the exact number of dashes that will fit on a line, so I've submitted a PR to fix this.