New bar line interface

New bar line interface

* the input string of a bar line called by \bar "<bar string>" resembles the output one-by-one; a repeat sign is called by ":|."

* (define-bar-line ...) or \defineBarLine allows for new definitions. These functions have four arguments, namely
  the bar line itself, the bar line used at the end of line, the bar line used at the begin of a new line and the span bar line.

* Annotations for barlines can be added to distinguish between two identical barlines with different break
  apperance or span bar lines.

* To align span bars properly, the space character " " has a
  special meaning. When it occurs, the width of the resembling glyph in the bar line definition is used.

* New glyphs can be added easily.

* Volta brackets take the bar line dimensions into account.