Drop support for Scala 2.10

[fthomas]

The same as #474 but rebased on current master.

[codecov]

Codecov Report

Merging #537 into master will increase coverage by 0.42%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #537      +/-   ##
==========================================
+ Coverage   94.27%   94.69%   +0.42%     
==========================================
  Files          62       59       -3     
  Lines         681      679       -2     
  Branches       10       11       +1     
==========================================
+ Hits          642      643       +1     
+ Misses         39       36       -3

Impacted Files	Coverage Δ
.../scala/eu/timepit/refined/macros/RefineMacro.scala	100% <ø> (ø)	⬆️
...la/eu/timepit/refined/macros/LiteralMatchers.scala	87.5% <ø> (ø)	⬆️
...rc/main/scala/eu/timepit/refined/api/Refined.scala	100% <ø> (ø)
...n/scala/eu/timepit/refined/macros/MacroUtils.scala	100% <ø> (ø)	⬆️

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