update to 0-based positional arguments

add samples

samples/memory.cr

@@ -0,0 +1,22 @@
+require "db"
+require "../src/sqlite3"
+
+DB.open "sqlite3", ":memory:" do |db|
+  db.exec "create table contacts (name string, age integer)"
+  db.exec "insert into contacts values (?, ?)", "John Doe", 30
+  db.exec "insert into contacts values (:name, :age)", {name: "Sarah", age: 33}
+
+  puts "max age:"
+  puts db.scalar "select max(age) from contacts" # => 33
+
+  puts "contacts:"
+  db.query "select name, age from contacts order by age desc" do |rs|
+    puts "#{rs.column_name(0)} (#{rs.column_name(1)})"
+    # => name (age)
+    rs.each do
+      puts "#{rs.read(String)} (#{rs.read(Int32)})"
+      # => Sarah (33)
+      # => John Doe (30)
+    end
+  end
+end

src/sqlite3/statement2.cr

@@ -13,7 +13,7 @@ class SQLite3::Statement2 < DB::Statement
   end
 
   protected def add_parameter(index : Int32, value)
-    bind_arg(index, value)
+    bind_arg(index + 1, value)
   end
 
   protected def add_parameter(name : String, value)