Remove optional plotting functionality and enable precompilation (#80)

* Remove optional plotting

The optional dependency on PyPlot and KernelDensity means that the
package was unable to support precompilation. Instead, plotting
integration should go in a separate package.

Closes #36.

* Enable precompilation

Author: ararslan

src/BenchmarkTools.jl

@@ -1,3 +1,5 @@
+__precompile__()
+
 module BenchmarkTools
 
 using Compat
@@ -68,12 +70,6 @@ export tune!,
        @belapsed,
        @btime
 
-##########################################
-# Plotting Facilities (loaded on demand) #
-##########################################
-
-loadplotting() = include(joinpath(dirname(@__FILE__), "plotting.jl"))
-
 #################
 # Serialization #
 #################