[RELASE] tag 0.7 release

[tqchen]

(Incomplete) list of changes, thanks to all contributors

• 0.6 is skipped because there are a lot of improvements since initial release
• More math operators
  • elementwise ops and binary ops
• Attribute support in computation graph
  • Now user can use attributes to give various hints about specific learning rate, allocation plans etc
• MXNet is more memory efficient
  • Support user defined memory optimization with attributes
• Support mobile applications by @antinucleon
• Refreshed update of new documents
• Model parallel training of LSTM by @tqchen
• Simple operator refactor by @tqchen
  • add operator_util.h to enable quick registration of both ndarray and symbolic ops
• Distributed training by @mli
• Support Torch Module by @piiswrong
  • MXNet now can use any of the modules from Torch.
• Support custom native operator by @piiswrong
• Support data types including fp16, fp32, fp64, int32, and uint8 by @piiswrong
• Support monitor for easy printing and debugging by @piiswrong
• Support new module API by @pluskid
  • Module API is a middle level API that can be used in imperative manner like Torch-Module
• Support bucketing API for variable length input by @pluskid
• Support CuDNN v5 by @antinucleon
• More applications
  • Speech recoginition by @yzhang87
  • Neural art by @antinucleon
  • Detection, RCNN bt @precedenceguo
  • Segmentation, FCN by @tornadomeet
  • Face identification by @tornadomeet
  • More on the example