Consider storing IDs as bytes

[bwaidelich]

Instead of

(new Column('id', Type::getType(Types::STRING)))
    ->setFixed(true)
    ->setLength(EventId::MAX_LENGTH)
    ->setCustomSchemaOptions($isSQLite ? [] : ['charset' => 'ascii']),

we could store the event id (and potentially causationId and correlationId) as binary:

(new Column('id', Type::getType(Types::BINARY)))
    ->setFixed(true)
    ->setLength(EventId::MAX_LENGTH)

Note:
For SQLite this is not supported (i.e. a table diff will always drop and re-add the column)
For PostgreSQL we could even use the UUID type (using DBALs Types::GUID abstraction)

Related: #12