Fixed locale issues in the vector classes' ConvertTo() methods

This could be regarded as a follow-up to #129.

This fixes the string output in Color.ConvertTo() and Vector{2,3,4}.ConvertTo(), by making the methods do what is advertised; that is, formatting a string representation of the vector with a specified CultureInfo.

This hasn't affected any titles I've come across thus far, but you just know some poor fellow would bump in it somewhere along the line.