GitLab

* Add early stopping for prediction

* Fix GBDT if-else prediction with early stopping

* Small C++ embelishments to early stopping API and functions

* Fix early stopping efficiency issue by creating a singleton for no early stopping

* Python improvements to early stopping API

* Add assertion check for binary and multiclass prediction score length

* Update vcxproj and vcxproj.filters with new early stopping files

* Remove inline from PredictRaw(), the linker was not able to find it otherwise

* expose save model to string to c_api

* add 'save-model-to-string' to python; use it to copy model

* remove boosting_type

1. add csc support
2. some data type from float to double

Categorical feature support (#108)

1. merge python-package
2. add dump model to json
3. fix bugs
4. clean code with pylint
5. update python examples

change static std::string to static char[]. (refer to https://google.github.io/styleguide/cppguide.html#Static_and_Global_Variables)