Remove bytes dependency & update Body constructors

[sagebind]

Remove bytes as a direct dependency, as our small usage does not really justify its inclusion. In addition, update the constructor methods for Body to reflect this change. These changes are minor but breaking, but encourage using the From traits more so as to reduce copying when possible.

[codecov]

Codecov Report

Merging #261 (8251f5d) into master (5212209) will decrease coverage by 0.01%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master     #261      +/-   ##
==========================================
- Coverage   71.86%   71.84%   -0.02%     
==========================================
  Files          49       49              
  Lines        2513     2515       +2     
==========================================
+ Hits         1806     1807       +1     
- Misses        707      708       +1     

Impacted Files	Coverage Δ
src/body.rs	74.62% <73.68%> (-0.76%)	⬇️
tests/redirects.rs	100.00% <100.00%> (ø)

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