Merge pull request go-gorp#315 from sourcegraph/v1

backport: Initialise plans using sync.Once

update supported go versions

Replace ginkgo with onpar (go-gorp#367)

We've been running in to more and more problems with ginkgo, and frankly, I prefer the simplicity of onpar.  Time to switch.

README updates

- Mention more infrequent changes
- Add CONTRIBUTING.md
- Mention maintainership in CONTRIBUTING.md

Merge pull request go-gorp#219 from sqdk/sqdk-patch-2-warn

Update gorp.go

columnToFieldIndex: revert b5ce3b9 change, as it breaks tag mapping w…

…hen a field marked transient matches a column mapped to another field. Fixes go-gorp#175 but reverses go-gorp#146

TestSelectAlias: modify to demonstrate how this behavior can be achieved using two separate structs - one that reflects the actual table structure (for inserts/updates) and one with the extended field, which can be used for selects.