Fix --raw with --chunked

[isidentical]

Resolves #1253. This is also a rewrite of the core uploading logic.

[codecov-commenter]

Codecov Report

Merging #1254 (b2032dd) into master (4d7d6b6) will decrease coverage by 0.76%.
The diff coverage is 94.83%.

@@            Coverage Diff             @@
##           master    #1254      +/-   ##
==========================================
- Coverage   97.28%   96.52%   -0.77%     
==========================================
  Files          67       85      +18     
  Lines        4235     5754    +1519     
==========================================
+ Hits         4120     5554    +1434     
- Misses        115      200      +85     

Impacted Files	Coverage Δ
tests/test_binary.py	100.00% <ø> (ø)
httpie/compat.py	31.11% <27.90%> (-68.89%)	⬇️
tests/conftest.py	77.14% <58.33%> (-9.82%)	⬇️
httpie/output/lexers/http.py	59.09% <59.09%> (ø)
tests/test_ssl.py	91.01% <66.66%> (-3.93%)	⬇️
httpie/output/lexers/common.py	75.00% <75.00%> (ø)
httpie/output/lexers/metadata.py	81.25% <81.25%> (ø)
httpie/manager/__main__.py	82.35% <82.35%> (ø)
httpie/models.py	93.93% <88.88%> (-3.43%)	⬇️
httpie/manager/core.py	92.85% <92.85%> (ø)
... and 68 more

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