Skip any number of header comment lines

[hersle]

Quick suggestion to generalize file reading to skip any number of header lines starting with # if nskip < 0.
The current format (and CAMB?) requires exactly 1 header line, but CLASS outputs 4 header lines.
This supports the old use case, and also makes it possible to directly use a $P(k)$ file from CLASS with COLA.

For example:

CLASSDIR="$HOME/hybrid-bias-cola-emulator/hi_class_public"
COLADIR="$HOME/hybrid-bias-cola-emulator/FML/FML/COLASolver"

mkdir /tmp/test_cola_class_input/
cd /tmp/test_cola_class_input/

cp $CLASSDIR/explanatory.ini .
cp $COLADIR/parameterfile.lua .

$CLASSDIR/class explanatory.ini
sed 's|input/example_power_spectrum_cb_z0.000.txt|output/explanatory00_pk.dat|' parameterfile.lua > parameterfile_class.lua
$COLADIR/nbody parameterfile_class.lua

...
#=====================================================
# Create initial conditions
#=====================================================
Skipping headerline: # Matter power spectrum P(k) at redshift z=0
Skipping headerline: # for k=1.04206e-05 to 5.30493 h/Mpc,
Skipping headerline: # number of wavenumbers equal to 556
Skipping headerline: #    1:k (h/Mpc)              2:P (Mpc/h)^3        
Line 0 : 1.04206e-05 48.3354 
Line 1 : 2.32697e-05 105.03 
Line 2 : 3.61637e-05 160.801 
Line 3 : 4.91373e-05 216.219 
Line 4 : 6.22254e-05 271.614 
Line 5 : 7.5464e-05 327.236 
Line 6 : 8.88903e-05 383.298 
Line 7 : 0.000102543 440.001 
Line 8 : 0.000116463 497.536 

#=====================================================
# Reading power-spectrum from ascii file [output/explanatory00_pk.dat]
# The P(k) is at the redshift: 0
# Using growth factors we scaled it to redshift: 20
# Found n: 556 lines in file (sample of it below):
#=====================================================
# k (h/Mpc)      P(k,zini)  (Mpc/h)^3    T(k,zini)  (Mpc)^2
1.04206e-05     0.177253        1.19132e+06    
0.00268339      34.4728         1.13778e+06    
0.00948356      80.701          946100         
0.0165519       92.1764         772646         
0.0237718       85.3579         624251         
0.0314024       71.3126         498798         
0.0405931       56.0828         390758         
0.0701943       36.1644         240853         
0.243622        4.96021         48903.6        
0.419948        1.70994         22073          
1.6776          0.0758284       2381.04        
...