If both upper_wall and lower_wall are True, `len(contour) // 2` rather
than `len(contour // 2)` should be used.

If a contour starts outside the wall then it can be that no
intersection is found. Handle that case, leaving original contour.

Method to plot single points, for interactive debugging

Attempting to handle cases where no intersection is found

Plots cell corners joined together, and cell centers as points.

Perhaps could use xlow, ylow points to provide a quadratic cell shape?

The idea is to first extend FineContour to the wall, then distort
PsiContour's points along the FineContour curve.

A divide-and-conquer algorithm is used to make finding intersections
with a large number of points efficient.

Move plotting to MeshRegion so individual regions can be plotted.
Mesh plotting methods iterate over and call MeshRegions.

Broke test case TestContour.test_append

FineContour.getPoint is the inverse of getDistance: It returns a
Point2D if given a distance along the FineContour

PsiContour.map takes a function that returns a distance shift, and
returns a new PsiContour that shares the FineContour with the
original. This will be used to perform mesh deformations.

If given, MeshRegion doesn't need to follow radial coordinate lines
and create PsiContours.

Enables mapping of the mesh points using shift functions.

Plots straight-sided cells connecting cell corners.

Added script plotting options to possible options list, so that
an exception isn't raised when they're used.

- Ensure that psi is passed to get_fine_contour
- Handle rounding errors near FineContour edges

Mesh.map() now creates an instance of self.__class__, so subclasses
including BoutMesh can be mapped.

Ensure that final index has ypos=1, to be consistent with upper_shift.
Prevent crossing lines from going off end of FineContour

MeshRegion.setWallIntersections(Equilibrium) calls
FineContour.setWallIntersections to calculate where contours
intsersect walls.

MeshRegion.wallAlignShiftFunction() creates a lambda function that
shifts a MeshRegion to align to the wall. That can map cells to have
zero size, but PsiContour.map prevents cells from crossing.

Change `axis` keyword to `ax` for consistency, return axis.

Use a polynomial basis to represent mesh point shifts within each
MeshRegion.

MeshRegionMapper generates new MeshRegion objects given a list of
polynomial coefficients. The order of the polynomials in X and Y
is set in the constructor.

MeshMapper uses MeshRegionMapper to generate new Mesh objects, using
a combined list of polynomial coefficients.

PsiContours that are shared between MeshRegions will in general
not be mapped in the same way. These PsiContours are averaged
in MeshMapper.generate to produce a consistent boundary between
regions.

Optimises meshes by varying the distortion parameters to minimise a
MeshMeasure. For now only one MeshMeasure: BoundaryDistance combines
distances between the mesh and the wall.

Enables the optimiser to take into account the orthogonality of the
mesh, by minimising tan(Beta) over the mesh, where Beta is the angle
between coordinate lines.

Can be used to disable some parts of Mesh construction in optimiser
loop.

Repeatedly creating regions and meshes, so reduce the amount of text
printed each iteration

- PoloidalSpacing measures the ratio of the poloidal size of
  neighbouring cells, penalising variations
- When PsiContours are merged on region boundaries, re-use the
  FineContour and distances that have already been calculated.
- Add __str__ methods to the MeshMeasure subclasses
- Add automatic optimisation to the `hypnotoad-geqdsk` script

- In optimisation loop only print every 20th iteration
- In hypnotoad-geqdsk script save the plotted cells to file

Changes some spacing, line breaks