feat: handle plus sign in scientific notation floats

[cvigilv]

This PR adds the ability to have floating number in scientific notation as follows:

1e+10
1E+10

Before, it would raise an error of the type:

problem with number read 1e, not a float number
problem with number read 1E, not a float number

Example:

julia> net = readnewick("((a:1,(b:1)):5,(c:1):1e+10);")
HybridNetwork, Rooted Network
6 edges
7 nodes: 3 tips, 0 hybrid nodes, 4 internal tree nodes.
tip labels: a, b, c
((a:1.0,(b:1.0)):5.0,(c:1.0):1.0e10);

To Do:

• Cover with unit tests

[cvigilv]

This is a draft PR since I'm unsure where to put the test. Please let me know and I'll do that.