Print simile marks

It is a common practise to use simile marks for repeated chords.
This simplifies the chord sheet and makes the actual chord changes more obvious.

%

Simile mark, playing instruction to repeat one preceding bar

%%

Simile mark, playing instruction to repeat the two preceding bars

Reprint preceding bars

Short cuts for the lazy ones to enter multiple bars of the same chords.

%1

Reprint the preceding bar

%2

Reprint two preceding bars

%4

Reprint four preceding bars

- Reprint a single bar
A B C %1

- Two reprint in a row
A B %1 %1

- Reprint two bars
A B %2

- Reprint 4 bars
A B C D
%4

- Simile marks
A B % %
E F %%