Add bindings (top-level "ufuncs") for predicates, measurement, etc.

[benbovy]

Some features available in s2geography that could be implemented in spherely with relatively little effort (i.e., straightforward functions returning simple types like bool, float, etc.):

Predicates:

• intersects
• equals
• contains
• touches
• within (add: some predicates #18)
• disjoint (add: some predicates #18)
• covers
• covered_by

Measurement:

• distance (s2geography link)
• area (s2geography link)
• length (s2geography link)

One example with intersects

s2geography API:

https://github.com/paleolimbot/s2geography/blob/764682d60f757383e5853a45a12404c84f3e5961/src/s2geography/predicates.h#L10-L12

spherely bindings:

spherely/src/predicates.cpp

Lines 37 to 51 in e874e60

	m.def("intersects",
	py::vectorize(Predicate(s2geog::s2_intersects)),
	py::arg("a"),
	py::arg("b"),
	R"pbdoc(
	Returns True if A and B share any portion of space.
	Intersects implies that overlaps, touches and within are True.
	Parameters
	----------
	a, b : :py:class:`Geography` or array_like
	Geography object(s)
	)pbdoc");

For predicates that are not directly implemented in s2geography but that can be easily derived from another predicate, it is possible to use a lambda, like for within:

spherely/src/predicates.cpp

Lines 84 to 100 in e874e60

	m.def("within",
	py::vectorize(Predicate([](const s2geog::ShapeIndexGeography& a_index,
	const s2geog::ShapeIndexGeography& b_index,
	const S2BooleanOperation::Options& options) {
	return s2geog::s2_contains(b_index, a_index, options);
	})),
	py::arg("a"),
	py::arg("b"),
	R"pbdoc(
	Returns True if A is completely inside B.
	Parameters
	----------
	a, b : :py:class:`Geography` or array_like
	Geography object(s)
	)pbdoc");

Documentation:

https://github.com/benbovy/spherely/blob/main/docs/api.rst#predicates

Typing annotations:

spherely/src/spherely.pyi

Line 104 in 0b7d3bb

intersects: _VFunc_Nin2_Nout1[Literal["intersects"], bool, bool]