Experimental 0.7 alpha

• Updated mxnet to 0.12.0rc1
• Include pretrained mobilenet models

Released models:

• mobilenet-608: mAP ~74.7, ~0.56s/frame on cpu
• mobilenet-512: mAP ~72.5, ~0.39s/frame on cpu
• resnet50-512: mAP ~79.1, ~1.0s/frame on cpu

Tested on i7-5557U CPU @ 3.10GHz, apple blas