Move exql to internal.

internal/sqladapter/collection.go

internal/sqladapter/database.go

internal/sqladapter/exql/column.go

internal/sqladapter/exql/column_test.go

internal/sqladapter/exql/column_value.go

internal/sqladapter/exql/column_value_test.go

internal/sqladapter/exql/columns.go

internal/sqladapter/exql/columns_test.go

internal/sqladapter/exql/database.go

internal/sqladapter/exql/database_test.go

internal/sqladapter/exql/default.go

internal/sqladapter/exql/group_by.go

internal/sqladapter/exql/group_by_test.go

internal/sqladapter/exql/hash.go

internal/sqladapter/exql/interfaces.go

internal/sqladapter/exql/join.go

internal/sqladapter/exql/join_test.go

internal/sqladapter/exql/order_by.go

internal/sqladapter/exql/order_by_test.go

internal/sqladapter/exql/raw.go