Add maintenance check in TibiadataHTMLDataCollectorV3

[tobiasehlert]

We need to have some way to detect maintenance mode and return some proper message.
This should be done in the TibiadataHTMLDataCollectorV3 function or somewhere more suitable.

Here is some initial logging at least:
https://github.com/TibiaData/tibiadata-api-go/blob/3f3aef1a9cbe9857143f4e971133f85239c4537d/src/webserver.go#L239-L245

[tobiasehlert]

This has been fixed in #34.

https://github.com/TibiaData/tibiadata-api-go/blob/78e658b7589f4a4b46c2fcdcc85d42f8332b1b6c/src/webserver.go#L259-L267