Update mask demo docs, add model download from paddlehub

* [DEMO] add mask detection demo, test=develop

* [DEMO] fix ssd detection demo bug, test=develop

* add cv image process

* fix arm liunx build error

* add LITE_WITH_CV defien to make cv, test=develop

* fix cv format, annd add describe in utils/cv

* set LITE_WITH_CV=OFF in build.sh, test=develop

* delete cv_enum.h in utils/cv, push the contents in cv_ennum.h to paddle_image_preprocess.h, test=develop

* according to reviews to redefine paddle_image_preprocess.h, test=develop

* add detailed note of flipParam, test=develop

* fix format in paddle_image_preprocess.h, test=develop

* fix cmake error in llite/CMakeLists.txt, missing mkdir cxx, test=develop

* according to review change, test=develop

* add elemetnwise mul constant elimination and deconv+relu, deconv+batchnorm fusion, test=develop

* fix format, test=develop

* fix model_optimize bug, update concat and split op, speed up, test=develop

* update split speed, test=develop

* fix format, test=develop

* add classify demo inn demo/cxx/ , test=develop

* fix formart inn mobile_classify, test=develop

* delete some note and extra code, test=develop

* remove test.jpg and labels.txt, test=develop

* add test_cv in cxx/demo

* add test_cv READMEE, test=develoop

* add note info, flip only support x, y, xy;rotate only support 90, 180, 270; test=develop

* fix build error, paddle_cv_arm , test=develop

* add GRAY to RGBA(BGRA) convert and RGBA(BGRA)_to_Tensor, test=develop

* fix format from review, test=develop

* fix makefile format. test=devellop

* fix bbuuild v7 error, test=develop

* [Demo] add cxx mobilenetv1-ssd detection demo, test=develop

* add makefile to mobile detection demo, test=develop

* [Demo] add cxx mobilenetv1-ssd detection demo, test=develop

* [demo] fix mobile_detection code style, test=develop

* [Demo] fix demo code style, test=develop

* [Demo] fix detection demo makefile dependency, test=develop