Adding Easy CRUD Support

[niting3c]

I wanted to add an easy way to perform CRUD for the users with transaction support. I already have a working code for the same that i used in another project and thought it would be better to add the support in here for everybody to use and contribute.

EXAMPLE :
https://github.com/niting3c/pgx/blob/5b90a3a1bb280eb68f9615ec8f8948cbd67bbfa4/internal/crud/crud.go#L2-L1

In future it can be enhanced by adding 'batch' operations as well.

Usage:
crud.GetOne(query,args... )
crud.Update(query,args ... )