v0.9.0

Constructors can be handed over as they are written, and the graph they
declare can be checked before anything is built (#3). Nothing existing
changes shape or behaviour; an upgrade cannot break a caller.

go doc -all against 0.8.0 adds Scope.Wire, Scope.Validate, Validation
with its Err method, and dihttp.Validate, and changes no signature. The
README no longer promises no reflection at all: Wire reads a constructor's
signature once at registration and calls it through reflect.Call; Provide
is as it was.

Added

• Scope.Wire[T](ctor) registers a plain constructor, func(A, B) T or
  func(A, B) (T, error), whose parameters are its dependencies. Each is
  resolved as a Provide closure would resolve it, from the same scope, so
  lifetimes, hooks, cycles and error paths are unchanged. The signature is
  read with reflection once at registration, where a constructor of the wrong
  shape is rejected like any other configuration error; a result merely
  assignable to T is accepted, so a concrete constructor can serve an
  interface key. The build calls the constructor through reflect.Call, about
  150ns and two allocations over a closure. Provide is untouched.
• Scope.Validate() walks the declared graph without building and returns a
  Validation: Errors (joined by Err()) for a dependency nothing provides,
  a cycle among Wire constructors, or a singleton that would build a Scoped
  service in a scope that cannot satisfy it; Owed for what a Scoped
  binding needs that the validating scope does not provide, since the scope
  resolving it may; Unchecked for the Provide closures.
• dihttp.Validate(app) validates from a throwaway request scope holding an
  *http.Request, so what a request scope would still miss is an error.