Implement chomp: option for gets, readline, readlines, each_line

[casperisfine]

It was added to IO methods in Ruby 2.4, but OpenSSL sockets don't have
them, so any code accepting SSL sockets can't make use of it.

Ref: ruby/ruby@a2144bd

cc @nobu since you implemented this in IO.

On another note, this led me to notice that SSLSocket#gets(nil) and SSLSocket#gets("") aren't supported either.

[nobu]

Seems fine.
The failure on mswin should be fixed by rebase.

[rhenium]

Thanks for working on this! This is indeed overlooked and should be implemented.

Unlike IO#gets, OpenSSL::Buffering/OpenSSL::SSL::SSLSocket#gets accepts a Regexp as the eol parameter. Should this be made compatible with chomp option too? Or perhaps it can simply be documented as unsupported... I didn't know #gets took a Regexp at all.

On another note, this led me to notice that SSLSocket#gets(nil) and SSLSocket#gets("") aren't supported either.

I think that should be aligned with IO too, as these currently don't give any useful return value.

[casperisfine]

Unlike IO#gets, OpenSSL::Buffering/OpenSSL::SSL::SSLSocket#gets accepts a Regexp as the eol parameter. Should this be made compatible with chomp option too?

um, so we'd need to chomp whatever the regexp matched? Seems tricky.