Reexport std and var from Statistics (#336)

* [docs] Call Statistics functions in same order as BenchmarkTools output

Moved `maximum` to immediately after `minimum`. This makes it easier to match-up the outputs against what `BenchmarkTools` prints.

* [docs] Note Statistics reexports

* Reexport std and var, remove unnecessary Statistics import

Author: milesfrain

docs/src/manual.md

@@ -353,7 +353,7 @@ BenchmarkTools.Trial
   allocs: Int64 19
 ```
 
-As you can see from the above, a couple of different timing estimates are pretty-printed with the `Trial`. You can calculate these estimates yourself using the `minimum`, `median`, `mean`, `maximum`, and `std` functions:
+As you can see from the above, a couple of different timing estimates are pretty-printed with the `Trial`. You can calculate these estimates yourself using the `minimum`, `maximum`, `median`, `mean`, and `std` functions (Note that `median`, `mean`, and `std` are reexported in `BenchmarkTools` from `Statistics`):
 
 ```julia
 julia> minimum(t)
@@ -363,6 +363,13 @@ BenchmarkTools.TrialEstimate:
   memory:           16.36 KiB
   allocs:           19
 
+julia> maximum(t)
+BenchmarkTools.TrialEstimate: 
+  time:             1.503 ms
+  gctime:           1.401 ms (93.21%)
+  memory:           16.36 KiB
+  allocs:           19
+
 julia> median(t)
 BenchmarkTools.TrialEstimate: 
   time:             30.818 μs
@@ -377,13 +384,6 @@ BenchmarkTools.TrialEstimate:
   memory:           16.36 KiB
   allocs:           19
 
-julia> maximum(t)
-BenchmarkTools.TrialEstimate: 
-  time:             1.503 ms
-  gctime:           1.401 ms (93.21%)
-  memory:           16.36 KiB
-  allocs:           19
-
 julia> std(t)
 BenchmarkTools.TrialEstimate: 
   time:             25.161 μs

src/BenchmarkTools.jl

@@ -36,6 +36,8 @@ export gctime,
     isimprovement,
     median,
     mean,
+    std,
+    var,
     rmskew!,
     rmskew,
     trim

test/GroupsTests.jl

@@ -2,7 +2,6 @@
 
 using BenchmarkTools
 using BenchmarkTools: TrialEstimate, Parameters
-using Statistics
 using Test
 
 seteq(a, b) = length(a) == length(b) == length(intersect(a, b))

test/TrialsTests.jl

@@ -1,7 +1,6 @@
 module TrialsTests
 
 using BenchmarkTools
-using Statistics
 using Test
 
 #########