Add raw header info to request object

[ahopkins]

Resolves #1963

This will add raw data from the header. Unit tests and final naming to come. I have been back and forth in my head about trying to keep it consistent with request.body. But, I also do not want to have to decode more than once. I might change my mind 4 more times before the PR is ready for review.

[codecov]

Codecov Report

Merging #2032 (55e095f) into master (c41d713) will increase coverage by 0.030%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master     #2032       +/-   ##
=============================================
+ Coverage   91.811%   91.842%   +0.030%     
=============================================
  Files           35        35               
  Lines         3224      3236       +12     
  Branches       556       556               
=============================================
+ Hits          2960      2972       +12     
  Misses         179       179               
  Partials        85        85               

Impacted Files	Coverage Δ
sanic/constants.py	100.000% <100.000%> (ø)
sanic/http.py	77.860% <100.000%> (+0.082%)	⬆️
sanic/mixins/routes.py	94.898% <100.000%> (ø)
sanic/request.py	97.924% <100.000%> (+0.067%)	⬆️
sanic/response.py	94.631% <100.000%> (+0.036%)	⬆️

---

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 c41d713...55e095f. Read the comment docs.

[ahopkins]

I pulled #2006 into this one. So, after that is merged this will be a much smaller PR.