[BUG] Multiline header in savetxt

[Bzero]

Describe the bug
When passing a header containing a linebreak to savetxt only the first line is a comment line, all following lines are uncommented.

ulab version: 6.7.2-2D

To Reproduce

np.savetxt('loadtxt.dat', np.array([1,2,3]), header='A header\nwith a second line')

The second line of the header is not a comment line:

# A header
with a second line
1.000000000000000
2.000000000000000
3.000000000000000

Expected behavior

The second line of the header should be a comment line as well as it is the case with numpy:

# A header
# with a second line
1.000000000000000
2.000000000000000
3.000000000000000

Additional context
Relevant for footers too.

[v923z]

This is really along the same lines as #709, thanks for pointing it out! I'll try to set a bit of time aside to fix this.

[Bzero]

Yes, sorry if I have been overreporting here a bit. I can try to address it myself as well.

[v923z]

Oh, don't worry! While these are similar issues, it's good that you've opened two tickets.

[v923z]

This is dealt with in #720.