Dynamic flags

[mwitkow]

Add flags with Set and Get functions that use atomic pointers to update values.

These are slightly slower, but guarantee race-free without locking.

Benchmark_Duration_Dyn_Get-8    1000000000           3.15 ns/op
Benchmark_Duration_Normal_get-8 2000000000           0.28 ns/op
Benchmark_Float64_Dyn_Get-8     1000000000           3.55 ns/op
Benchmark_Float64_Normal_Get-8  2000000000           0.45 ns/op
Benchmark_Int64_Dyn_Get-8       1000000000           3.39 ns/op
Benchmark_Int64_Normal_Get-8    2000000000           0.37 ns/op
Benchmark_String_Dyn_Get-8      100000000           41.5 ns/op
Benchmark_String_Normal_get-8   100000000           36.2 ns/op

This should fix #3