Add some basic exports (#22)

Currently this just exports the very basics, with minimal chance of name
collision with other packages and/or user code.

Author: ararslan

src/ChainRules.jl

@@ -6,6 +6,8 @@ using Base.Broadcast: materialize, materialize!, broadcasted, Broadcasted, broad
 
 import NaNMath, SpecialFunctions, LinearAlgebra, LinearAlgebra.BLAS
 
+export AbstractRule, Rule, frule, rrule
+
 include("differentials.jl")
 include("rules.jl")
 include("rules/base.jl")

src/rules.jl

@@ -244,7 +244,7 @@ unary input, unary output scalar function:
 ```julia-repl
 julia> x = rand();
 
-julia> sinx, dsin = ChainRules.frule(sin, x);
+julia> sinx, dsin = frule(sin, x);
 
 julia> sinx == sin(x)
 true
@@ -258,7 +258,7 @@ unary input, binary output scalar function:
 ```julia-repl
 julia> x = rand();
 
-julia> sincosx, (dsin, dcos) = ChainRules.frule(sincos, x);
+julia> sincosx, (dsin, dcos) = frule(sincos, x);
 
 julia> sincosx == sincos(x)
 true
@@ -300,7 +300,7 @@ unary input, unary output scalar function:
 ```julia-repl
 julia> x = rand();
 
-julia> sinx, dx = ChainRules.rrule(sin, x);
+julia> sinx, dx = rrule(sin, x);
 
 julia> sinx == sin(x)
 true
@@ -314,7 +314,7 @@ binary input, unary output scalar function:
 ```julia-repl
 julia> x, y = rand(2);
 
-julia> hypotxy, (dx, dy) = ChainRules.rrule(hypot, x, y);
+julia> hypotxy, (dx, dy) = rrule(hypot, x, y);
 
 julia> hypotxy == hypot(x, y)
 true

test/runtests.jl

@@ -1,10 +1,10 @@
 # TODO: more tests!
 
 using ChainRules, Test, FDM, LinearAlgebra, Random
-using ChainRules: rrule, frule, extern, accumulate, accumulate!, store!, @scalar_rule,
+using ChainRules: extern, accumulate, accumulate!, store!, @scalar_rule,
     Wirtinger, wirtinger_primal, wirtinger_conjugate, add_wirtinger, mul_wirtinger,
     Zero, add_zero, mul_zero, One, add_one, mul_one, Casted, cast, add_casted, mul_casted,
-    DNE, Thunk, Casted, Wirtinger
+    DNE, Thunk, Casted
 using Base.Broadcast: broadcastable
 
 include("test_util.jl")