[#163] Fix zip streaming

[KirillovDenis]

Declined to use (*zip.Writer).CreateRaw() as it does not result in a noticeable performance increase, but introduces unnecessary complexity.

Increased buffer to download zip archive up to 3MB (the same as for upload files).
Started using (*fasthttp.RequestCtx).SetBodyStreamWriter() to get rid of of accumulation of response body in application memory.

close #163
Signed-off-by: Denis Kirillov [email protected]

[codecov]

Codecov Report

Merging #164 (d28d8b8) into master (67ea967) will increase coverage by 13.08%.
The diff coverage is 26.00%.

@@             Coverage Diff             @@
##           master     #164       +/-   ##
===========================================
+ Coverage   14.22%   27.31%   +13.08%     
===========================================
  Files           3       11        +8     
  Lines         253      875      +622     
===========================================
+ Hits           36      239      +203     
- Misses        213      604      +391     
- Partials        4       32       +28     

Impacted Files	Coverage Δ
downloader/head.go	0.00% <0.00%> (ø)
metrics.go	0.00% <0.00%> (ø)
pprof.go	0.00% <0.00%> (ø)
uploader/multipart.go	0.00% <ø> (ø)
uploader/upload.go	0.00% <0.00%> (ø)
downloader/download.go	7.22% <10.10%> (+2.43%)	⬆️
main.go	34.37% <45.45%> (ø)
app.go	56.80% <58.06%> (ø)
settings.go	52.11% <85.71%> (ø)
uploader/filter.go	85.71% <94.87%> (ø)
... and 9 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0a0af13...d28d8b8. Read the comment docs.