Create `@fprototype` and update code to use it

This macro removes types from a function declaration so that there's no risk of other overloads being seen as less specific by Julia's overload resolution.

Examples:

@fprototype do_thing(t::AbstractMyType, data::T)::Tuple{T, Int} = error() turns into do_thing(t, data) = error()
@fprototype do_thing(t::AbstractMyType) turns into function do_thing end

heyx3 / Bplus.jl

Create `@fprototype` and update code to use it #93