*: move github.com/pingcap/tidb/parser here

[tiancaiamao]

Here is the dependency graph:

TiDB need to update its "import github.com/pingcap/tidb/parser" to "import github.com/pingcap/parser"

[tiancaiamao]

@shenli

[kennytm]

Question about package management... As parser.go isn't checked in, do the dependencies still need to manually make parser and check it into their vendor/*?

[tiancaiamao]

parser.go will be included in this repository, although I didn't do it in this commit @kennytm