odbc: Support connection with attribute key-value pairs

`connect()` now accepts an attribute table to construct a connection string
for `SQLDriverConnect()`. It supports three forms now:

1. The original form
```lua
connect(source, user, pass)
```

2. Connect with the DSN keyword
```lua
connect {
  DSN = source,
  UID = user,
  PWD = pass,
}
```
or
```lua
connect({ DSN = source }, user, pass)
```

3. Connect with the DRIVER keyword
```lua
connect {
  DRIVER = "SQL Server",
  SERVER = ".\\SQLEXPRESS",
  UID = user,
  PWD = pass,
}
```
or
```lua
connect({
  DRIVER = "SQL Server",
  SERVER = ".\\SQLEXPRESS",
}, user, pass)
```

src/ls_odbc.c

@@ -1075,9 +1075,12 @@ static int create_connection (lua_State *L, int o, env_data *env, SQLHDBC hdbc)
 */
 static int env_connect (lua_State *L) {
 	env_data *env = (env_data *) getenvironment (L, 1);
-	SQLCHAR *sourcename = (SQLCHAR*)luaL_checkstring (L, 2);
+	SQLCHAR *sourcename = lua_istable(L, 2) ? NULL : (SQLCHAR*)luaL_checkstring (L, 2);
 	SQLCHAR *username = (SQLCHAR*)luaL_optstring (L, 3, NULL);
 	SQLCHAR *password = (SQLCHAR*)luaL_optstring (L, 4, NULL);
+	luaL_Buffer b;
+	int k;
+	int v;
 	SQLHDBC hdbc;
 	SQLRETURN ret;
 
@@ -1086,9 +1089,58 @@ static int env_connect (lua_State *L) {
 	if (error(ret))
 		return luasql_faildirect (L, "connection allocation error.");
 
-	/* tries to connect handle */
-	ret = SQLConnect (hdbc, sourcename, SQL_NTS, 
-		username, SQL_NTS, password, SQL_NTS);
+	if (sourcename != NULL)
+	{
+		/* tries to connect handle */
+		ret = SQLConnect (hdbc, sourcename, SQL_NTS, 
+			username, SQL_NTS, password, SQL_NTS);
+	}
+	else
+	{
+		lua_pushnil(L);
+		k = lua_gettop(L);
+		lua_pushnil(L);
+		v = lua_gettop(L);
+
+		luaL_buffinit(L, &b);
+
+		lua_pushnil(L);
+		while (lua_next(L, 2))
+		{
+			lua_replace(L, v);
+			lua_replace(L, k);
+			lua_pushvalue(L, k);
+			luaL_addvalue(&b);
+			luaL_addchar(&b, '=');
+			lua_pushvalue(L, v);
+			luaL_addvalue(&b);
+			luaL_addchar(&b, ';');
+			lua_pushvalue(L, k);
+		}
+
+		if (username != NULL)
+		{
+			luaL_addlstring(&b, "UID", 3);
+			luaL_addchar(&b, '=');
+			lua_pushvalue(L, 3);
+			luaL_addvalue(&b);
+			luaL_addchar(&b, ';');
+		}
+		if (password != NULL)
+		{
+			luaL_addlstring(&b, "PWD", 3);
+			luaL_addchar(&b, '=');
+			lua_pushvalue(L, 4);
+			luaL_addvalue(&b);
+			luaL_addchar(&b, ';');
+		}
+
+		/* tries to connect handle */
+		ret = SQLDriverConnect(hdbc, NULL,
+			luaL_buffaddr(&b), (SQLSMALLINT)luaL_bufflen(&b),
+			NULL, 0, NULL, SQL_DRIVER_NOPROMPT);
+	}
+
 	if (error(ret)) {
 		ret = fail(L, hDBC, hdbc);
 		SQLFreeHandle(hDBC, hdbc);