support raw based holder

[invisal]

Add the support for positional placeholder and named placeholder. You can now use

connection.raw("SELECT * FROM tbl WHERE id = ?", [1]);

Or

connection.raw("SELECT * FROM tbl WHERE id = :id", { id: 1 });

Test Case

  √ Positional placeholder (6 ms)
  √ Positional placeholder inside the string should be ignored
  √ Named placeholder to number placeholder
  √ Named placeholder to number placeholder with string (1 ms) 
  √ Named placeholder with missing value should throw an error (11 ms)
  √ Number of positional placeholder should match with the number of values (1 ms)      
  √ Mixing named and positional placeholder should throw error (1 ms)
  √ Convert positional placeholder to numbered placeholder (1 ms) 

Connection Test Case

  √ Support named parameters
  √ Support positional placeholder