Fix compiler warnings across project

[sloshy]

Some code used features of Scala or http4s that either were deprecated, or confused the compiler while being technically usable. This tweaks the code that's there just enough to get it all working without warnings.

• No more procedure syntax
• Pattern matching casts are now done explicitly
• http4s client .fetch syntax is deprecated, replaced w/ .run.use
• Replace ? with * for kind projector usage

[codecov]

Codecov Report

Merging #422 (b214738) into master (db771e0) will increase coverage by 0.32%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #422      +/-   ##
==========================================
+ Coverage   67.55%   67.88%   +0.32%     
==========================================
  Files           8        8              
  Lines         299      302       +3     
  Branches        5        6       +1     
==========================================
+ Hits          202      205       +3     
  Misses         97       97              

Impacted Files	Coverage Δ
fetch-debug/src/main/scala/document.scala	0.00% <ø> (ø)
fetch/src/main/scala/fetch.scala	89.70% <100.00%> (+0.15%)	⬆️

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[rafaparadela]

Not sure about the explicit casting, but as long as removing compilation warnings is the motivation, I'm ok with that :-)
Thanks for the efforts.