all: rename functions, deprecate old ones

Rename get_by_* to user_by_* and get_all to users. users() now can return errors.

pwd_test.v

@@ -1,17 +1,17 @@
 // vtest build: !windows
 import pwd
 
-fn test_get_by_uid() {
-	pw := pwd.get_by_uid(0)!
+fn test_user_by_uid() {
+	pw := pwd.user_by_uid(0)!
 	assert pw.name == 'root'
 }
 
-fn test_get_by_name() {
-	pw := pwd.get_by_name('root')!
+fn test_user_by_name() {
+	pw := pwd.user_by_name('root')!
 	assert pw.uid == 0
 }
 
-fn test_get_all() {
-	pws := pwd.get_all()
+fn test_users() {
+	pws := pwd.users()!
 	assert pws.len > 0
 }