Solves issue #6

[ribosaki]

A new perl script named "feed_venn_labels.pl" has been created that generates an ascii input file with the same format as before with the following modification:
The lines indicating the number of elements for each group can hold in addition a label for that circle. A blank space separates the number and the label (which continues until the end of the line).
So these two files would be for equivalent diagrams, except that the second one contains labels:

=============
nVenn v1.2
3
Group1
Group2
Group3
0
2
1
2
3
0
1
1

nVenn v1.2
3
Group1
Group2
Group3
0
2 z, x
1 f
2 g, h
3 c, d, e
0
1 b
1 a

The main.cpp has modified in order to parse correctly both types of input files. In addition the class borderLine has been extended to include a vector of strings containing the labels for each circle. The printing of these labels to the svg plot has been added in function toSVG().
The most tricky part has been to properly assign the labels to the corresponding circle, as the binMap does not follow "standard binary order". This assignment has been done inside the function setCircles(...).

The documentation has not been updated for this change, as it is unsure if this modification will be included into the main branch.