assign_map: Assign edges to the hex grid
In mrc-ide/PlasmoMAPI: Mapping Plasmodium Spatial Connectivity from Genetic Data

Given an PlasmoMAPI project with a hex map already created, determine which edges intersect each hex. Assumes an elliptical projection with the start- and end-points of an edge becoming the two foci of an ellipse.

assign_map(
  proj,
  eccentricity = 0.9,
  report_progress = TRUE,
  pb_markdown = FALSE
)

`proj`	object of class `pm_project`.
`eccentricity`	eccentricity of ellipses, defined as half the distance between foci divided by the semi-major axis. e = sqrt{1 - b^2/a^2}, where e is the eccentricity, a is the length of the semi-major axis, and b is the length of the semi-minor axis. Eccentricity ranges between 0 (perfect circle) and 1 (straight line between foci).
`report_progress`	if `TRUE` then a progress bar is printed to the console during the permutation testing procedure.
`pb_markdown`	whether to run progress bars in markdown mode, in which case they are updated once at the end to avoid large amounts of output.