New analyses - collinearity

Added the following analyses

1. Collinearity, defined as (\mathbf{\hat{n} \cdot \hat{b}})^2, where also the tangent vector has been normalised.
2. An alternative definition of twist, removing the assumption that \mathbf{u} is orthogonal to \mathbf{\hat{T}} (See Kamien's review). This is stored in twist_alt. This definition uses the normal to the ring, \mathbf{\hat{n}}, and divides the integrand by 1-(\mathbf{\hat{n}\cdot \hat{b}})^2 The result appears to be more linear, but not too much. I need to write down the derivation.