Changelog

Major refactor — modernized engine, new API, and rich plotting.

Projection engine switched from reproj to gdalraster::transform_xy(). All projection work is now a single batched GDAL call.
API renamed: proj.in/proj.out → source/target, following reproj conventions. target is the second positional argument (required); source defaults to "EPSG:4326".
tissot() input is now any “xy-ish” object (matrix, data.frame, list, length-2 vector) via the internal as_xy() helper. The old lambda/phi positional arguments are replaced by x.
tissot() returns a tissot_tbl (subclassed tibble) with source and target stored as attributes. Column names changed to: x, y, dx_dlam, dy_dlam, dx_dphi, dy_dphi, scale_h, scale_k, scale_omega, scale_a, scale_b, scale_area, angle_deformation, convergence.
indicatrix() returns an indicatrix_list (replaces indicatrixes class). Accepts tissot_tbl or raw coordinates + explicit target.
Removed: indicatrix0(), tissot0(), .prj(), and the internal numericDeriv path. The Jacobian is now computed directly via finite differences.

plot.indicatrix() and plot.indicatrix_list() with:
- Reference unit circle overlay (show.circle)
- Lambda/phi direction axes (show.axes)
- show.circle and show.axes accept TRUE, FALSE, or a named list of graphical parameters for full customization
- Colour-coded fill via fill.by (e.g. "scale_area", "angle_deformation")
print() and summary() methods for tissot_tbl.
print(), length(), and [ methods for indicatrix_list.
tissot_map() and tissot_abline() accept explicit target argument.
as_xy() internal helper coerces diverse coordinate inputs.
resolve_gpar() internal helper for the logical-or-list graphical parameter pattern.

tissot 0.2.0