Change stdlib imports to use std prefix in most examples (#17202)

lib/impure/db_mysql.nim

@@ -31,7 +31,7 @@
 ## ----------------------------------
 ##
 ## .. code-block:: Nim
-##     import db_mysql
+##     import std/db_mysql
 ##     let db = open("localhost", "user", "password", "dbname")
 ##     db.close()
 ##
@@ -56,7 +56,7 @@
 ##
 ## .. code-block:: Nim
 ##
-##  import db_mysql, math
+##  import std/[db_mysql, math]
 ##
 ##  let theDb = open("localhost", "nim", "nim", "test")
 ##

lib/impure/db_odbc.nim

@@ -37,7 +37,7 @@
 ## ----------------------------------
 ##
 ## .. code-block:: Nim
-##     import db_odbc
+##     import std/db_odbc
 ##     var db = open("localhost", "user", "password", "dbname")
 ##     db.close()
 ##
@@ -62,7 +62,7 @@
 ##
 ## .. code-block:: Nim
 ##
-##  import db_odbc, math
+##  import std/[db_odbc, math]
 ##
 ##  var theDb = open("localhost", "nim", "nim", "test")
 ##

lib/impure/db_postgres.nim

@@ -47,7 +47,7 @@
 ## To use Unix sockets with `db_postgres`, change the server address to the socket file path:
 ##
 ## .. code-block:: Nim
-##   import db_postgres ## Change "localhost" or "127.0.0.1" to the socket file path
+##   import std/db_postgres ## Change "localhost" or "127.0.0.1" to the socket file path
 ##   let db = db_postgres.open("/run/postgresql", "user", "password", "database")
 ##   echo db.getAllRows(sql"SELECT version();")
 ##   db.close()
@@ -64,7 +64,7 @@
 ## ----------------------------------
 ##
 ## .. code-block:: Nim
-##     import db_postgres
+##     import std/db_postgres
 ##     let db = open("localhost", "user", "password", "dbname")
 ##     db.close()
 ##

lib/impure/db_sqlite.nim

@@ -35,7 +35,7 @@
 ##
 ## .. code-block:: Nim
 ##
-##    import db_sqlite
+##    import std/db_sqlite
 ##
 ##    # user, password, database name can be empty.
 ##    # These params are not used on db_sqlite module.
@@ -66,7 +66,7 @@
 ##
 ## .. code-block:: nim
 ##
-##    import db_sqlite, math
+##    import std/[db_sqlite, math]
 ##
 ##    let db = open("mytest.db", "", "", "")
 ##
@@ -99,7 +99,7 @@
 ##
 ## .. code-block:: nim
 ##
-##   import random
+##   import std/random
 ##
 ##   ## Generate random float datas
 ##   var orig = newSeq[float64](150)

lib/impure/nre.nim

@@ -26,7 +26,7 @@ when defined(js):
 ##
 ## .. code-block:: nim
 ##
-##    import nre except toSeq
+##    import std/nre except toSeq
 ##
 ##
 ## Licencing

lib/impure/re.nim

@@ -274,7 +274,7 @@ proc match*(s: string, pattern: Regex, matches: var openArray[string],
   ## returned.
   ##
   runnableExamples:
-    import sequtils
+    import std/sequtils
     var matches: array[2, string]
     if match("abcdefg", re"c(d)ef(g)", matches, 2):
       doAssert toSeq(matches) == @["d", "g"]
@@ -494,7 +494,7 @@ iterator split*(s: string, sep: Regex; maxsplit = -1): string =
   ## Substrings are separated by the regular expression `sep`
   ## (and the portion matched by `sep` is not returned).
   runnableExamples:
-    import sequtils
+    import std/sequtils
     doAssert toSeq(split("00232this02939is39an22example111", re"\d+")) ==
       @["", "this", "is", "an", "example", ""]
   var last = 0