make it possible to type multi-line code

[Aliaksandr Rahalevich]

[kwanhur]

you can place repl.start() at multi lines.
just like this

content_by_lua_block {
local repl = require('resty.repl')
repl.start()
ngx.log(ngx.NOTICE, 'repl pass one')
repl.start()
ngx.log(ngx.NOTICE, 'repl pass again')
}

then use repl.stop() to go into next point.