* Turn xgboost::DataType into C++11 enum class
* New binary serialization format for DMatrix::MetaInfo
* Fix clang-tidy
* Fix c++ test
* Implement new format proposal
* Move helper functions to anonymous namespace; remove unneeded field
* Fix lint
* Add shape.
* Keep only roundtrip test.
* Fix test.
* various fixes
* Update data.cc
Co-authored-by: Jiaming Yuan <jm.yuan@outlook.com>
* Move get transpose into cc.
* Clean up headers in host device vector, remove thrust dependency.
* Move span and host device vector into public.
* Install c++ headers.
* Short notes for c and c++.
Co-Authored-By: Philip Hyunsu Cho <chohyu01@cs.washington.edu>