✨ should split "std" into submodules

[Antisunny]

as demonstrated below:

import {split, lines} from "std/text"
import {replace_once, replace} from "std/macro"
import {dir_exist, file_exist, file_read} from "std/fs"
import {sum} from "std/num"
import {includes} from "std"

[b1ek]

this would also introduce a breaking change. imo now is the right time to do this, before amber gets widely adopted

[Ph0enixKM]

This should be also adopted now since std library is not officially documented yet

[Mte90]

#152

[Mte90]

I did a new PR #291 that fix some stuff and it is updated with the latest changes