Several onText handlers register

[khudaibirdin]

Hi!
When I try to describe onText handler:

bot.Handle(tele.OnText, handler.OnText1)
bot.Handle(tele.OnText, handler.OnText2)
bot.Handle(tele.OnText, handler.OnText3)

I only describe last handler.OnText3 handler, because of:

type Bot struct {
...
handlers    map[string]HandlerFunc
...
}

in Bot struct.

Maybe realize possibility to add the slice of several handler functions.
When detecting handler by OnText it would be processed by all handlers in slice.

[nullcache]

Since tele.OnXXX can only be registered once, I implemented an internal router to manage the registrations.