Modification of documentation for convolutional encoding

[icyveins7]

The Trellis function has the argument for the generator polynomial marked as

g_matrix : 2D ndarray of ints (octal representation)

i.e. base 8 polynomial. This is extremely misleading as the actual argument expected is that of a standard base 10 integer (the function calls the utility function dec2bin). This doesn't cause problems in the examples as the polynomials used there are less than 8, but upon implementing anything with longer memory the output was all wrong and caused a big headache.

Suggestion: amend the documentation to denote g_matrix as base 10.