[myank] Improve data token handling at start end end of myanked section

[WolfgangDrescher]

Closes #71

Adds support for chords at start and end of a score filtered with myank and now keep all signifiers (e.g. ll for terminal long notes were removed).

Chord example

Source:

**kern
*M4/4
=1
1c 1e 1g
=2
1d 1f 1a
=3
1e 1g 1b
=4
1f 1a 1cc
=5
1g 1b 1dd
==
*-

=> myank -m 2-3

**kern
*M4/4
=2
1d 1f 1a
=3
1e 1g 1b
=
*-

Signifier example

Source:

**kern
*M4/4
=1
1c
=2
1d
=3
1e
=4
1f
=5
1gll
==
*-

=> myank -l 12-12

**kern
*M4/4
=5
1gll
==
*-

---

0a07e11 handles some special cases such as:

Before:

After: