Change the package manager to go modules

[zier-one]

What problem does this PR solve?

Change the package manager to go modules

What is changed and how it works?

we can use go mod to manage dependencies,old 'make xxx' command still work.
we can delete the 'vendor' dir,go mod and makefile will help us handle it

[WangXiangUSTC]

why remove vendor? I think we can keep it

[zier-one]

why remove vendor? I think we can keep it

i think it is redundant.
when we use 'make build' or 'make test',it can help us download dependencies and copy them to vendor.we can use vendor as usual,but i think it‘s not necessary to commit vendor in git repo,vendor shouldn't be managed by go.mod and git repo, however only be managed by go.mod.

[IANTHEREAL]

vendor is cache here. consider network downloads in china

[zier-one]

vendor is cache here. consider network downloads in china

ok,this is a reason that is difficult to refuse

[kennytm]

Must we use TiDB 2.0.8 or could we use the master version to get rid of the yacc parser?

[IANTHEREAL]

I think we should use master version in master branch. This repo would release with TiDB after 2.1 ga consistently

[IANTHEREAL]

LGTM

[WangXiangUSTC]

we can run a script to clean these file, you can see hack/clean_vendor.sh in tidb

[zier-one]

already fix it

[WangXiangUSTC]

LGTM

[tiancaiamao]

Could go get work with this repo now?