Keep the batch size even in strategy generator.

[Antlera]

Now we just calculate straight forward updated batch size from original batch size in strategy generator.
There are multiple libraries optimized for batch_size in the power of 2. (e.g. 2、4、8、16、32). It‘s reasonable to set an even batch size.

[Antlera]

However, there are mystical problems mentioned by some blogs. That is to say, we may experience unexpected slow down by setting an even number batch size.