Improve benchmarking and examples (#37)

* Use @Btime and fixed `out` assignment

* Improved replaceBase macro examples

- Remove extra dot in the macro arguments for ^ and / operators.
- Added benchmark example for ^

Author: tk3369

README.md

@@ -37,23 +37,30 @@ To avoid naming conflicts with Base, methods are not exported and so need to
 be accessed via the namespace:
 ```julia
 using AppleAccelerate
-X = randn(1_000_000)
-@time Y = exp(X) # standard libm function
-@time Y = AppleAccelerate.exp(X) # Accelerate array-oriented function
+using BenchmarkTools
+X = randn(1_000_000);
+@btime exp.($X); # standard libm function
+@btime AppleAccelerate.exp($X); # Accelerate array-oriented function
 ```
 
 The `@replaceBase` macro replaces the relevant Base methods directly
 ```julia
+@btime sin.($X); # standard libm function
 AppleAccelerate.@replaceBase sin cos tan
-AppleAccelerate.@replaceBase(.^, ./) # use parenthesised form for infix ops
-@time sin(X) # will use AppleAccelerate methods for vectorised operations
+@btime sin($X);  # will use AppleAccelerate methods for vectorised operations
+
+X = randn(1_000_000);
+Y = fill(3.0, 1_000_000);
+@btime $X .^ $Y;
+AppleAccelerate.@replaceBase(^, /) # use parenthesised form for infix ops
+@btime $X ^ $Y;
 ```
 
 Output arrays can be specified as first arguments of the functions suffixed
 with `!`:
 ```julia
-out = Array(Float64,1_000_000)
-@time AppleAccelerate.exp!(out, X)
+out = zeros(Float64, 1_000_000)
+@btime AppleAccelerate.exp!($out, $X)
 ```
 
 **Warning**: no dimension checks are performed on the `!` functions, so ensure