Add something like `input_interactive!`

[statiolake]

For interactive problem, OnceSource won't work as expected. To use proconio in such problems we need to explicitly specify LineSource for the source of input!. Preparing a macro that always uses LineSource may be helpful.

[vvforekk]

I think this feature is helpful for especially users who is not familiar with proconio's internal implementation. I would like to work on this, may I create a PR for you?

[statiolake]

Of course :) Thanks.