orm: skip via the "-" attribute

vlib/orm/orm.v

@@ -446,6 +446,12 @@ pub fn orm_table_gen(table string, q string, defaults bool, def_unique_len int,
 		}
 		for attr in field.attrs {
 			match attr.name {
+				'sql' {
+					// [sql:'-']
+					if attr.arg == '-' {
+						is_skip = true
+					}
+				}
 				'primary' {
 					primary = field.name
 				}
@@ -470,13 +476,13 @@ pub fn orm_table_gen(table string, q string, defaults bool, def_unique_len int,
 				}
 				'sql_type' {
 					if attr.kind != .string {
-						return error("sql_type attribute need be string. Try [sql_type: '${attr.arg}'] instead of [sql_type: ${attr.arg}]")
+						return error("sql_type attribute needs to be string. Try [sql_type: '${attr.arg}'] instead of [sql_type: ${attr.arg}]")
 					}
 					ctyp = attr.arg
 				}
 				'default' {
 					if attr.kind != .string {
-						return error("default attribute need be string. Try [default: '${attr.arg}'] instead of [default: ${attr.arg}]")
+						return error("default attribute needs to be string. Try [default: '${attr.arg}'] instead of [default: ${attr.arg}]")
 					}
 					if default_val == '' {
 						default_val = attr.arg

vlib/orm/orm_test.v

@@ -23,6 +23,7 @@ struct User {
 	name            string [sql: 'username']
 	is_customer     bool
 	skipped_string  string [skip]
+	skipped_string2 string [sql: '-']
 }
 
 struct Foo {
@@ -59,6 +60,8 @@ fn test_use_struct_field_as_limit() {
 	}!
 
 	assert users.len == 1
+	assert users[0].skipped_string == ''
+	assert users[0].skipped_string2 == ''
 }
 
 fn test_orm() {

vlib/v/gen/c/json.v

@@ -528,6 +528,7 @@ fn (mut g Gen) gen_struct_enc_dec(utyp ast.Type, type_info ast.TypeInfo, styp st
 			match attr.name {
 				'json' {
 					if attr.arg == '-' {
+						// [json:'-']
 						is_skip = true
 					} else {
 						name = attr.arg