Do not override builtin method help()

[OctoNezd]

The echobot2 example overrides builtin method help(). This PR renames the help(update, context) function to help_command(update, context).

Perhaps change start to start_command too?

[Bibo-Joshi]

Personally, I don't see a need to change start, as that's not builtin. But would you mind checking the other examples, too?

[OctoNezd]

The only other examples that used help() are inllinebot and inlinekeyboard. Both updated now.

[Bibo-Joshi]

Thanks for you contribution!