Add new tool to mark sections of a kern score

[WolfgangDrescher]

To highlight certain moments or sections in a score, I currently often use small JavaScript functions. Since this is unreliable, especially with spine splits, I have now added a tool called notemark. So you can easily highlight certain parts in the browser by adding a line !!!filter: notemark -l 19 or something similar before the score is rendered with Verovio.

notemark is perhaps not the best naming. I am open to better suggestions. How about notemarker or notehighlight?

Currently the highlighting of notes is only supported via line numbers. In the future it might be useful to implement support for measures or beat segments.

test.krn:

**kern	**kern	**kern	**kern
*clefF4	*clefGv2	*clefG2	*clefG2
*k[f#]	*k[f#]	*k[f#]	*k[f#]
*M3/4	*M3/4	*M3/4	*M3/4
4GG	4B	4d	4g
=1	=1	=1	=1
4G	4B	4d	2g
4E	8cL	4e	.
.	8BJ	.	.
4F#	4A	4d	4dd
=2	=2	=2	=2
4G	4G	2d	4.b
4D	4F#	.	.
.	.	.	8a
4E	4G	4B	4g
=3	=3	=3	=3
4C	8cL	8eL	4.g
.	8BJ	8d	.
8BBL	4c	8e	.
8AAJ	.	8f#J	8a
4GG	4d	4g	4b
=4	=4	=4	=4
2D;	2d;	2f#;	2a;
==	==	==	==
*-	*-	*-	*-

notemark test.krn -l 19:

**kern	**kern	**kern	**kern
*clefF4	*clefGv2	*clefG2	*clefG2
*k[f#]	*k[f#]	*k[f#]	*k[f#]
*M3/4	*M3/4	*M3/4	*M3/4
4GG	4B	4d	4g
=1	=1	=1	=1
4G	4B	4d	2g
4E	8cL	4e	.
.	8BJ	.	.
4F#	4A	4d	4dd
=2	=2	=2	=2
4G	4G	2d	4.b
4D	4F#	.	.
.	.	.	8a
4E	4G	4B	4g
=3	=3	=3	=3
4C	8cL	8eL	4.g@
.	8BJ	8d	.
8BBL@	4c@	8e@	.
8AAJ	.	8f#J	8a
4GG	4d	4g	4b
=4	=4	=4	=4
2D;	2d;	2f#;	2a;
==	==	==	==
*-	*-	*-	*-
!!!RDF**kern: @ = marked note color="#ef4444"

notemark test.krn -l 11-15 -k 1,4

**kern	**kern	**kern	**kern
*clefF4	*clefGv2	*clefG2	*clefG2
*k[f#]	*k[f#]	*k[f#]	*k[f#]
*M3/4	*M3/4	*M3/4	*M3/4
4GG	4B	4d	4g
=1	=1	=1	=1
4G	4B	4d	2g
4E	8cL	4e	.
.	8BJ	.	.
4F#	4A	4d	4dd
=2	=2	=2	=2
4G@	4G	2d	4.b@
4D@	4F#	.	.
.	.	.	8a@
4E@	4G	4B	4g@
=3	=3	=3	=3
4C	8cL	8eL	4.g
.	8BJ	8d	.
8BBL	4c	8e	.
8AAJ	.	8f#J	8a
4GG	4d	4g	4b
=4	=4	=4	=4
2D;	2d;	2f#;	2a;
==	==	==	==
*-	*-	*-	*-
!!!RDF**kern: @ = marked note color="#ef4444"