Add RETURNING to Delete statement.

Add DELETE statement wiki page.

wiki/DELETE.md

@@ -0,0 +1,58 @@
+DELETE statement deletes rows that satisfy the WHERE clause from the specified table. More about delete statement
+in PostgreSQL: https://www.postgresql.org/docs/11/sql-delete.html
+
+Following clauses are supported:
+- WHERE(delete_condition) - Only rows for which delete condition returns true will be deleted.
+- RETURNING(output_expression...) - An expressions to be computed and returned by the DELETE command after each row is deleted. 
+The expression can use any column names of the table. Write _TableName_.AllColumns to return all columns.
+
+### Example
+
+```
+// delete all links with name 'Gmail' and 'Outlook'
+deleteStmt := Link.
+    DELETE().
+    WHERE(Link.Name.IN(String("Gmail"), String("Outlook")))
+```
+
+Debug sql of above statement:
+
+```sql
+DELETE FROM test_sample.link      -- test_sample is name of the schema
+WHERE link.name IN ('Gmail', 'Outlook');
+```
+
+### Execute statement
+
+To execute delete statement and get sql.Result:
+
+```
+res, err := deleteStmt.Exec(db)
+```
+
+To execute delete statement and return records deleted, 
+delete statement has to have RETURNING clause:
+
+```
+deleteStmt := Link.
+    DELETE().
+    WHERE(Link.Name.IN(String("Gmail"), String("Outlook"))).
+    RETURNING(Link.AllColumns)
+    
+dest := []model.Link{}
+
+err := deleteStmt.Query(db, &dest)
+    
+```
+
+Use `ExecContext` and `QueryContext` to provide context object to execution.
+
+##### SQL table used for the example:
+```sql
+CREATE TABLE IF NOT EXISTS link (
+    id serial PRIMARY KEY,
+    url VARCHAR (255) NOT NULL,
+    name VARCHAR (255) NOT NULL,
+    description VARCHAR (255)
+);
+```

wiki/INSERT.md

@@ -9,7 +9,9 @@ Following clauses are supported:
 - MODEL(model) - list of values for columns will be extracted from model object
 - MODELS([]model)  - list of values for columns will be extracted from list of model objects
 - QUERY(select) - select statement that supplies the rows to be inserted.
-- RETURNING(columns...) - list of columns to return as statement result
+- RETURNING(output_expression...) - An expressions to be computed and returned by the INSERT statement after each row is inserted.
+The expressions can use any column names of the table. Write _TableName_.AllColumns to return all columns.
+
 
 _This list might be extended with feature Jet releases._ 
 
@@ -124,7 +126,7 @@ err := insertStmt.Query(db, &dest)
 
 Use `ExecContext` and `QueryContext` to provide context object to execution.
 
-Insert example SQL table:
+##### SQL table used for the example:
 ```sql
 CREATE TABLE IF NOT EXISTS link (
     id serial PRIMARY KEY,

wiki/UPDATE.md

@@ -1,12 +1,13 @@
 UPDATE changes the values of the specified columns in all rows that satisfy the condition.
 More about UPDATE statement in PostgreSQL: https://www.postgresql.org/docs/11/sql-update.html
 
-Following clauses are supported 
+Following clauses are supported:
 - UPDATE(columns...) - list of columns to update
 - SET(values...) - list of values for columns
 - MODEL(model) - list of values for columns will be extracted from model object
-- WHERE(condition) - row condition to update
-- RETURNING(columns...) - list of columns to return as statement result
+- WHERE(condition) - only rows for which condition returns true will be updated.
+- RETURNING(output_expression...) - An expressions to be computed and returned by the UPDATE statement after each row is updated.
+The expressions can use any column names of the table. Write _TableName_.AllColumns to return all columns.
 
 _This list might be extended with feature Jet releases._ 
 
@@ -23,7 +24,7 @@ updateStmt := Link.
 Debug sql of above statement:
 ```sql
 UPDATE test_sample.link          -- 'test_sample' is name of the schema
-SET (name, url) = ('Bong', 'http://bong.com')
+SET (name, url) = ('Yahoo', 'http://yahoo.com')
 WHERE link.name = 'Bing';
 ```
 
@@ -41,8 +42,8 @@ updateStmt := Link.
     WHERE(Link.Name.EQ(String("Bing")))
 ```
 
-`Link.Name, Link.URL, Link.Description` - can be replaced with Link.MutableColumns. All columns minus primary key columns.
-Primary key columns are not updated usually.
+`Link.Name, Link.URL, Link.Description` - can be replaced with Link.MutableColumns(all columns minus primary key column).  
+Primary key columns usually are not updated.
 
 ```
 updateStmt := Link.
@@ -75,7 +76,7 @@ err := updateStmt.Query(db, &dest)
 
 Use `ExecContext` and `QueryContext` to provide context object to execution.
 
-Update example SQL table:
+##### SQL table used for the example:
 ```sql
 CREATE TABLE IF NOT EXISTS link (
     id serial PRIMARY KEY,