Pass metadata along with stream creation command

[trueinsider]

In our program different streams should be handled differently in a non-deterministic way. To determine how exactly each stream should be handled we're passing metadata along with it's creation command. I believe others too can benefit from such feature and it's optional and don't break API.

[codecov-io]

Codecov Report

Merging #46 into master will decrease coverage by 0.85%.
The diff coverage is 70.58%.

@@            Coverage Diff            @@
##           master     #46      +/-   ##
=========================================
- Coverage   84.46%   83.6%   -0.86%     
=========================================
  Files           5       5              
  Lines         470     482      +12     
=========================================
+ Hits          397     403       +6     
- Misses         64      69       +5     
- Partials        9      10       +1

Impacted Files	Coverage Δ
stream.go	89.78% <100%> (+0.22%)	⬆️
session.go	77.12% <61.53%> (-1.51%)	⬇️

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[xtaci]

why not just send metadata as the first few bytes？

[trueinsider]

that would be a separate packet then, which requires handling in case of error, etc. in this case you 100% have metadata once stream is open which quite simplifies code.

[trueinsider]

@xtaci can you please look at this again?

[xtaci]

@xtaci can you please look at this again?
as I said before, you can just just send metadata as the first few bytes of the streams.