Add support for different INT sizes to MysqlAdapter, refs #249

- add `$limit` parameter to `AdapterInterface::getSqlType`, allowing more complex type hinting
- additional column sizes for "text" and "integer" types now determined by `MysqlAdapter::getSqlType`
- `$limit` is passed through `getSqlType`

Cleans up a some of the changes made in #330:

- remove `PHINX_TYPE_*` constants from `AdapterInterface`
- deprecate `TEXT_SMALL` in favor of `TEXT_TINY` in `MysqlAdapter`
- remove the `classifyTextColumn` method in `MysqlAdapter`
`Column::getLimit` is no longer used here, all limits are passed through `getSqlType`. This prevents accidentally adding a limit to (eg) a `blob` type column.