Create braid directly from ODE

[jeanluct]

(Spinoff of #124.)

Have the braid constructor take a function handle as an argument, which could then be used to call ode45 and generate the braid.

Example:

b = braid(@func,tspan,XY0);  % create braid of trajectories starting at XY0

Syntax is meant to mimic ode45. Could even pass optional ode45 options at the end. The RHS function @func only takes one trajectory at a time, and XY0 is a set of n initial conditions. (XY0 should have dimension [2 n], to agree with the XY constructor.)

An implementation might involve going through by pairs of strings, and setting and @events function for when the x coordinates coincide.

[jeanluct]

Started implementing this on iss126-braid-from-ODE branch.

[jeanluct]

Some more thoughts about this:

• Should the function create an XY array, then pass it to colobraiding? Or better, it could generate the crosscell object and pass it to the private function sortcross2gen.
• Better to integrate pairwise or all the particles at ones? Pairwise then we generate crosscell. Otherwise we get an XY array. My feeling is that pairwise scales better. In fact I think that's what we'd found when MDF first developed the pairwise crossing method.

[jeanluct]

Continued to implement this. 2d721e4 is a reasonable prototype. It surprisingly slow, however, compared to equally-spaced sampling. Maybe that's a feature of the simple flow I'm using.