More json type features support

[juneszh]

The json type is an important feature starting from MySQL 5.7 and is becoming more and more popular, but it is not well experienced in the use of Medoo. So I have some preliminary ideas:

1. Add [$] tag to implement json path, like column[$] or column[$.a]

   $database->select("t", "c[$.name]"); // select c->"$.name" from t;

   $database->select("t", "c", ["c[$.name]" => "ben"]); // select c from t where c->"$.name" = "ben";

   $database->select("t", "c", ["c[$.age][>]" => 18]); // select c from t where c->"$.age" > 18;

2. Add ->json function to implement modify json values

   $database->json->insert("t", ["c[$.sex]" => "female"]); // update t set c = JSON_INSERT(c, "$.sex", "female");

   $database->json->set("t", ["c[$.sex]" => "male"]); // update t set c = JSON_SET(c, "$.sex", "male");

   $database->json->replace("t", ["c[$.sex]" => "male"]); // update t set c = JSON_REPLACE(c, "$.sex", "male");

   $database->json->remove("t", ["c[$.sex]" => "male"]); // update t set c = JSON_REMOVE(c, "$.sex", "male");

3. Medoo::raw support JSON_CONTAINS, JSON_LENGTH, JSON_OVERLAPS and so on

   $database->select("t", "c", [Medoo::raw("JSON_CONTAINS(c, 'nick', '$.child')") => 1]); // select c from t where JSON_CONTAINS(c, 'nick', '$.child') = 1;

   $database->select("t", "c", [Medoo::raw("JSON_LENGTH(c, '$.child')") => 0]); // select c from t where JSON_LENGTH(c, '$.child') = 0;

   but Medoo::raw return object that cannot be the key of the array, maybe change the return to string with json_encode