use ncnnoptimize to optimize model

the typical usage

ncnnoptimize mobilenet.param mobilenet.bin mobilenet-opt.param mobilenet-opt.bin 65536 

operator fusion

• batchnorm - scale
• convolution - batchnorm
• convolutiondepthwise - batchnorm
• deconvolution - batchnorm
• deconvolutiondepthwise - batchnorm
• innerproduct - batchnorm
• convolution - relu
• convolutiondepthwise - relu
• deconvolution - relu
• deconvolutiondepthwise - relu
• innerproduct - relu

eliminate noop operator

• innerproduct - dropout
• flatten after global pooling

prefer better operator

• replace convolution with innerproduct after global pooling