Changelog for tree-sitter-0.8.0.0

Use a shared Token type for anonymous leaves in generated AST types.
Allow generated ASTs to override the representation for portions of the AST by defining specialized datatypes. Note that this should be used sparingly to keep the maintenance burden of the AST types low.
Generate named sum types as newtype wrappers around sums constructed with :+:.
Generate named & anonymous sum types as balanced binary trees of :+:s instead of right-chained lists.
Rename the bytes field of leaves to text.

Unmarshal has been split into Unmarshal, UnmarshalAnn, and UnmarshalField, with the first newly taking type constructors of kind * -> *. UnmarshalAnn can be used to unmarshal annotation types relating to the entire node, and UnmarshalField can be used to unmarshal fields of zero or more nodes.
UnmarshalAnn instances are provided for the semantic-source types Loc, Range, and Span.
AST datatypes are generated with GHC.Generics.:+: for anonymous sums in field positions instead of Eithers. This makes it possible to define typeclasses over them at kind * -> * instead of only at kind *.
AST datatypes receive derived instances of Foldable, Functor, Generic, Generic1, and Traversable.

Node has a nodeIsExtra field stating whether it was produced via the extras rule.