Support compression in forward transfer

[repeatedly]

Experimental implementation.

Adding compress true in out_forward configuration.

[dhiltonp]

Can we get feedback on this PR? Is it going to be merged? Is there a reason for it to not be merged? Is there something that needs to be fixed in this code before it is accepted?

Thanks!

[repeatedly]

We need feedback on several enviroment for checking performance and compression ratio with actual logs.
I post it on #504 but there is no feedback so I'm pending the merge.

[repeatedly]

BTW, now this branch conflicts with master.
I will update the patch later.

[repeatedly]

rebased for testing.

[tagomoris]

At least, this change doesn't include tests.

[repeatedly]

Yes because we need test with production traffic.
If this change is useful, I will add tests.

BTW, I will rebase this branch.

[Manikantan22]

Do we still have "compress true" for out_forward plugin?

I am using td-agent2 and tried to use compress true but getting below error in logs.

[warn]: parameter 'compress' in is not used.

[repeatedly]

compress doesn't support yet in the upstream
because this patch is not merged yet.

[tagomoris]

This feature will be supported with compressed buffer. Pending.

[repeatedly]

#1179 is more better way. I close this PR.