Add length function to segment

[orena1]

Hi,
A segment already has a volume() and area() functions, why not add also a length function.
I know it is easy to calculate the length of a segment, but if it already has those two function I think that for completeness it would be good to also add the length function.

Thanks

[nrnhines]

@ramcdougal What do you think? seg.length() as alternative to

seg.sec.L/seg.sec.nseg

I used the function form as one cannot change the segment length directly. Not much additional
benefit as sec.L/sec.nseg gives the values for all the segments in the section except that
sec(0) and sec(1) have a length of 0.

[ramcdougal]

I like this idea.

I also think sections should gain area and volume methods.