Release 0.2.0

Scalar is now num-dual's trait, blanket-implemented, rather than a
hand-rolled one declaring the same methods over a fixed list of types.

Breaking: the `autodiff` feature is gone, since num-dual is no longer
optional; `Scalar::re`, `exp`, `ln`, `log10`, `sqrt`, `sin`, `cos`,
`powi`, `powf`, `abs` and `powt` are gone, replaced by DualNum,
DualStruct and Signed, with `powt` now `powd`; and a call built only
from float literals must name its scalar, as gtd7d::<f64>(..).

Not breaking, but the reason it is worth doing: a caller's own dual type
is now covered automatically, and the dependency tree drops from about
twenty crates to two.

Cargo.lock

@@ -325,7 +325,7 @@ dependencies = [
 
 [[package]]
 name = "nrlmsise00"
-version = "0.1.0"
+version = "0.2.0"
 dependencies = [
  "approx",
  "criterion",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "nrlmsise00"
-version = "0.1.0"
+version = "0.2.0"
 edition = "2021"
 authors = ["Connor Johnstone"]
 description = "NRLMSISE-00 atmosphere model, generic over its scalar type so density can be differentiated"