Add deprecated messages for cis and cispi (#96)

* add deprecated messages for cis and cispi

* add `@test_deprecated` for cis

* update depwarn messages for cis and cispi

Author: hyrodium

src/Quaternion.jl

@@ -178,11 +178,19 @@ if VERSION ≥ v"1.6"
     !!! Note
         This is not equivalent to `exp(π*im*q)`. See [cis(::Quaternion)](@ref) for details.
     """
-    Base.cispi(q::Quaternion) = extend_analytic(cispi, q)
+    function Base.cispi(q::Quaternion)
+        Base.depwarn("`cispi(::Quaternion)` is deprecated and will be removed in the next breaking release. See https://github.com/JuliaGeometry/Quaternions.jl/pull/76 for more information.", :cispi)
+        extend_analytic(cispi, q)
+    end
+end
+
+function Base.cis(q::Quaternion)
+    Base.depwarn("`cis(::Quaternion)` is deprecated and will be removed in the next breaking release. See https://github.com/JuliaGeometry/Quaternions.jl/pull/76 for more information.", :cis)
+    extend_analytic(cis, q)
 end
 
 for f in (
-    :sqrt, :exp, :exp2, :exp10, :expm1, :log2, :log10, :log1p, :cis,
+    :sqrt, :exp, :exp2, :exp10, :expm1, :log2, :log10, :log1p,
     :sin, :cos, :tan, :asin, :acos, :atan, :sinh, :cosh, :tanh, :asinh, :acosh, :atanh,
     :csc, :sec, :cot, :acsc, :asec, :acot, :csch, :sech, :coth, :acsch, :asech, :acoth,
     :sinpi, :cospi,

test/Quaternion.jl

@@ -410,8 +410,8 @@ Base.:(/)(a::MyReal, b::Real) = a.val / b
                 ]
                     @test f(q) ≈ finv(inv(q))
                 end
-                @test cis(q) ≈ exp(normalize(q - real(q)) * q)
-                VERSION ≥ v"1.6" && @test cispi(q) ≈ cis(π * q)
+                @test @test_deprecated(cis(q)) ≈ exp(normalize(q - real(q)) * q)
+                VERSION ≥ v"1.6" && @test @test_deprecated(cispi(q)) ≈ cis(π * q)
             end
         end