Add support for custom types to ddl2cpp

[matthijs]

See issue #106

Add three possible ways for mapping columns to user-defined types.

1. By using --path-to-cpp-types <csv>
2. Inline SQL leading comments
3. PostgreSQL extension: handle unmodified pg_dump output

I haven't checked where mysqldump or sqlite3 puts the comments. If you have an example of how that looks I can try to fix that too.

A somewhat unrelated change but it caused me a headache, add the possibility to strip the schema from the table (pg_dump includes the schema in the CREATE TABLE statement).

And of course, updated the documentation.

[rbock]

Thanks, this looks pretty cool already!

Can you add some tests, too?

MySQL dump with comment:

DROP TABLE IF EXISTS `tab_foo`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!50503 SET character_set_client = utf8mb4 */;
CREATE TABLE `tab_foo` (
  `id` bigint NOT NULL AUTO_INCREMENT,
  `text_nn_d` varchar(255) NOT NULL DEFAULT '',
  `int_n` int DEFAULT NULL COMMENT 'cpp_type:test::my_int',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
/*!40101 SET character_set_client = @saved_cs_client */;

sqlite3 does not seem to support column comments officially, see docs. But it seems to happily accept comments in the same way as MySQL above.

[matthijs]

I've updated the MR based on your comments.

Also added a note about the sqlite backend. According to what I found on internet only inline comments are supported (and preserved when dumped).

[rbock]

Nice! Thanks for the super swift implementation, the support for multiple options, and the clean documentation!