Use base64 (via glib) instead of plain char cast.
Remove ascii_to_poly() since it's unreliable (we don't
really know how many polynomials we will need
for a string).
The function returns a newly allocated poynom of the string size * 7
7 bits per ASCII symbol.
the function need to be warped so the maximal poynom is corresponding to
the NTRU context.
