clean up and document register macro

Author: mileslucas

src/Polynomials.jl

@@ -17,7 +17,6 @@ include("polynomials/Poly.jl") # Deprecated -> Will be removed
 include("pade.jl")
 include("deprecated.jl")
 
-
 # Interface for all AbstractPolynomials
 include("common.jl")
 

src/abstract.jl

@@ -14,6 +14,23 @@ An abstract container for various polynomials.
 abstract type AbstractPolynomial{T<:Number} end
 
 
+"""
+    Polynomials.@register(name)
+
+Given a polynomial with `name`, creates some common convenience constructors and conversions to minimize code required for implementation of a new polynomial type.
+
+# Example
+```julia
+struct MyPolynomial{T} <: AbstractPolynomial{T} end
+
+Polynomials.@register MyPolynomial
+```
+
+# Implementations
+This will implement simple self-conversions like `convert(::Type{MyPoly}, p::MyPoly) = p` and creates two promote rules. The first allows promotion between two types (e.g. `promote(Polynomial, ChebyshevT)`) and the second allows promotion between parametrized types (e.g. `promote(Polynomial{T}, Polynomial{S})`). 
+
+For constructors, it implements the shortcut for `MyPoly(...) = MyPoly{T}(...)`, singleton constructor `MyPoly(x::Number, ...)`, and conversion constructor `MyPoly{T}(n::S, ...)`.
+"""
 macro register(name)
     poly = esc(name)
     quote
@@ -37,6 +54,5 @@ macro register(name)
         $poly(n::Number, var = :x) = $poly([n], var)
         $poly{T}(n::S, var = :x) where {T,S<:Number} = $poly(T(n), var)
         $poly{T}(x::AbstractVector{S}, var = :x) where {T,S<:Number} = $poly(T.(x), var)
-
     end
 end

src/polynomials/Poly.jl

@@ -5,7 +5,7 @@ of `Polynomial`
 
 export Poly
 
-struct Poly{T} <: AbstractPolynomial{T}
+struct Poly{T<:Number} <: AbstractPolynomial{T}
     coeffs::Vector{T}
     var::Symbol
     function Poly(a::AbstractVector{T}, var::SymbolLike = :x) where {T <: Number}