Initial broadcast support

repl/command.go

repl/repl.go

repl/set.go

storage/broadcast.sql.go

storage/display.go

storage/migrations/1_create_table.up.sql

storage/models.go

storage/queries/broadcast.sql

storage/queries/system.sql

storage/standard.sql.go

storage/system.sql.go

storage/users.sql.go

this/broadcast.go

this/this.go