Fix dead links in quick start after reorganzing documentaion directory

Bazel protobuf and gtest

Do not use https://github.com/pubref/rules_protobuf, but use https://github.com/google/protobuf/ as external dependency for protobuf

Remove sudo from Dockerfile.*

test code for issue #729

remove breathe and doc/howto/source directory

Support predicting the samples from sys.stdin

Fix dead link after rearrange english documentation.

Correctly handling multiple calls to parse_config()

Install libgtest-dev in Dockerfiles

add semantic_role_labeling_cn.md

* Fix #803

Add bazel installation to the Dockerfiles

Add SIMD flags for runtime check

Refine use_concepts.rst

Fix nvcc stray character Issue #760

add file extensions in doc/