Add Future::join and Future::try_join

[abhishekc-sharma]

Addresses #470 .

@yoshuawuyts Regarding the module level documentation changes, is the plan to replace join! and try_join! in the documentation with join and try_join ?

[ghost]

I like this change. 👍

To be honest, I don't find join! and try_join! all that useful nor expect those macros to pop up in practice. It seems a lot of people are confused by future joining in general (see here).

Instead, I expect people will spawn futures to make them run in paralle/concurrently rather than joining futures.

wdyt, @yoshuawuyts?

[yoshuawuyts]

@stjepang you might be right actually. Agree we can probably remove them without much loss.

[abhishekc-sharma]

I have changed the reference to join! and try_join! in the module documentation to refer to join and try_join functions instead.

[ghost]

@yoshuawuyts @portgasd666 In that case, let's also remove macros join! and try_join! in this PR? :)

[yoshuawuyts]

thanks!