allow _ for spaces

(easier to use in browsers/shells where spaces lead to unwanted
behaviour, e.g. starting a search or ending an argument)

src/bahnhofname.gleam

@@ -14,6 +14,7 @@ import gleam/map.{Map}
 import gleam/uri
 import gleam/hackney
 import gleam/pair.{swap}
+import gleam/result
 import mist
 
 const ds100_domain = "ds100.bahnhof.name"
@@ -99,6 +100,7 @@ fn unpercent(encoded: String) -> String {
     |> list.prepend(bit_string.from_string(head))
     |> bit_string.concat
     |> bit_string.to_string
+    |> result.map(fn (str) { string.replace(str, "_", " ") })
   res
 }