readable symbol links

[tayloraswift]

this eradicates all but one hash-disambiguated symbol link from this package’s documentation by using type signature based disambiguation instead.

the one remaining holdout is the Int.init(_:) method, which Int inherits from SignedInteger. this link collides with a similar method on FixedWidthInteger which also uses the name T for its generic parameter, albeit with completely different generic constraints.

error: selector 'Int.init(_:) (T)' is ambiguous

Since we just want to cast the grayscale samples directly to index values, we don’t need the palette parameter, so we discard it with the `_` binding. We then return the ``Int.init(_:) (T)`` initializer, which casts the grayscale samples to ``Int``s.
                                                                                                                                                                              ~~~~~~~~~~~~~~~^

note: did you mean 'Int.init(_:) [4EKVL]'? ((extension in Swift):Swift.SignedInteger< where A: Swift.FixedWidthInteger>.init<A where A1: Swift.BinaryInteger>(A1) -> A)
note: did you mean 'Int.init(_:) [6GT9Z]'? ((extension in Swift):Swift.FixedWidthInteger.init<A where A1: Swift.BinaryFloatingPoint>(A1) -> A)
note: did you mean 'Int.init(_:) (Float16) -> ()'? (Swift.Int.init(Swift.Float16) -> Swift.Int)
note: did you mean 'Int.init(_:) (NSNumber) -> ()'? ((extension in Foundation):Swift.Int.init(Foundation.NSNumber) -> Swift.Int)
note: did you mean 'Int.init(_:) (Float) -> ()'? (Swift.Int.init(Swift.Float) -> Swift.Int)
note: did you mean 'Int.init(_:) (CGFloat) -> ()'? ((extension in Foundation):Swift.Int.init(Foundation.CGFloat) -> Swift.Int)
note: did you mean 'Int.init(_:) (Double) -> ()'? (Swift.Int.init(Swift.Double) -> Swift.Int)
note: did you mean 'Int.init(_:) (Float80) -> ()'? (Swift.Int.init(Swift.Float80) -> Swift.Int)
note: did you mean 'Int.init(_:) (String) -> ()'? ((extension in Swift):Swift.FixedWidthInteger.init(Swift.String) -> Swift.Optional<A>)

i worked around this by spelling out Int’s ``SignedInteger/init(_:)`` in English, but this is a little icky.