Making it easy to initialize the EF6 MiniProfiler

The EF6 Miniprofiler can now be easily registered with the following
code:

// Add the using
using StackExchange.Profiling.EntityFramework6;

// Initialize EF6 MiniProfiler
MiniProfilerEF6.Initialize();
Merge pull request #12 from stebet/master

Making it easy to initialize the EF6 MiniProfiler with `MiniProfilerEF6.Initialize();`