Add new tool to output original line numbers

[WolfgangDrescher]

Some of the older programs (e.g. beat) sometimes make some lines of the kern score disappear. In order to be able to create a mapping between the original line numbers, I have created a program lnnr with which the line numbers can be displayed as new **lnnr spines.

test.krn:

!!!OTL: Test
**kern
*clefG2
*M4/4
=
!local comment
4c
4d
4e
4f
=
!!global comment
4g
4a
4h
4cc
==
*-

lnnr test.krn

!!!OTL: Test
**kern	**lnnr
*clefG2	*
*M4/4	*
=	=
!local comment	!
4c	7
4d	8
4e	9
4f	10
=	=
!!global comment
4g	13
4a	14
4h	15
4cc	16
==	==
*-	*-

lnnr test.krn --index --prepend

!!!OTL: Test
**lnidx	**kern
*	*clefG2
*	*M4/4
=	=
!	!local comment
6	4c
7	4d
8	4e
9	4f
=	=
!!global comment
12	4g
13	4a
14	4h
15	4cc
==	==
*-	*-