Add vendor to improve building speed.

This also adds ability to be built in network-constrained environment.

vendor/github.com/bytedance/sonic/.gitignore

@@ -0,0 +1,52 @@
+*.o
+*.swp
+*.swm
+*.swn
+*.a
+*.so
+_obj
+_test
+*.[568vq]
+[568vq].out
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+_testmain.go
+*.exe
+*.exe~
+*.test
+*.prof
+*.rar
+*.zip
+*.gz
+*.psd
+*.bmd
+*.cfg
+*.pptx
+*.log
+*nohup.out
+*settings.pyc
+*.sublime-project
+*.sublime-workspace
+.DS_Store
+/.idea/
+/.vscode/
+/output/
+/vendor/
+/Gopkg.lock
+/Gopkg.toml
+coverage.html
+coverage.out
+coverage.xml
+junit.xml
+*.profile
+*.svg
+*.out
+ast/test.out
+ast/bench.sh
+
+!testdata/*.json.gz
+fuzz/testdata
+*__debug_bin