Remove implicit conversions from state to ask and tell

[LukaJCB]

This should resolve #31

[codecov-io]

Codecov Report

Merging #83 into master will decrease coverage by 0.33%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #83      +/-   ##
==========================================
- Coverage   91.09%   90.75%   -0.34%     
==========================================
  Files          63       62       -1     
  Lines         539      530       -9     
  Branches        3        3              
==========================================
- Hits          491      481      -10     
- Misses         48       49       +1

Impacted Files	Coverage Δ
core/src/main/scala/cats/mtl/instances/state.scala	84.21% <0%> (-5.27%)	⬇️

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[andyscott]

Approving on the basis of a sound code change. I can't speak to the overall design change other than reading the related issue and noting that this sounds reasonable!