* dialect/sql/schema: add method to create a named versioned migration file
* doc/md: documentation for named versioned migrations
* entc/gen/template/dialect/sql/feature: add NamedDiff method to create named versioned migration files
* all: go generate
* doc/md: apply CR
* dialect/sql/schema: fix go doc
* all: update atlas
* dialect/sql/schema: diff connected DB and defined schema and write changes to migration file
* dialect/sql/schema: use migration directory and formatter directly instead of a planner
* all: update atlas
* cmd: add command to create a new migration file
* entc/gen: generate main.go with migrate diff example
* all: regenerate
* cmd/internal/base: make linter happy
* all: support Go 1.16 in versioned migrations main.go
* entc/gen: put versioned migrations behind feature flag
* all: regenerate
* cmd/ent: driver-prefixed dsn in migrate diff command
* cmd/internal/base: remove prefix from migrate import
* cmd/internal/base: use cobra.CheckErr
* cmd: remove diff command
* entc/gen/template/dialect/sql/feature: remove generated main.go
* all: rebase on master and go mod tidy
* all: regenerate
