Add syntax module

[NeQuissimus]

I could have used this a lot today, so I am finally getting around to contributing a syntax module :)

Basically, these return refined types for a few methods on NonEmptyString.
Also, I added a string interpolator that creates NonEmptyString.

Anybody is welcome to add to this, I may provide more convenience syntax as I need it.

Notes: I know virtually nothing about Scala.js or Scala.Native. I created the cross-build targets but am unsure whether they should exist...

Edit: Removed Scaja.js and Scala.Native. Looks like the string interpolator does not work there

[codecov]

Codecov Report

Merging #589 into master will decrease coverage by 0.04%.
The diff coverage is 90%.

@@            Coverage Diff             @@
##           master     #589      +/-   ##
==========================================
- Coverage   93.08%   93.04%   -0.05%     
==========================================
  Files          65       66       +1     
  Lines         709      719      +10     
  Branches       11       11              
==========================================
+ Hits          660      669       +9     
- Misses         49       50       +1

Impacted Files	Coverage Δ
.../main/scala/eu/timepit/refined/syntax/string.scala	90% <90%> (ø)

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[fthomas]

Thanks for this, @NeQuissimus! I'd vote to move the NonEmptyStringOps into the core module since it doesn't need new dependencies. And instead of refined-syntax I'd call the new module refined-contextual.

I've also worked on extension methods for NonEmptyString here https://github.com/fthomas/refined/compare/topic/NonEmptyString.Syntax but hadn't time to polish it. The methods there are available without any additional import because NonEmptyString.Syntax is mixed into the implicit scope of NonEmptyString. Not sure if this is the way to go, but it was nice to see that it is possible. Maybe you've any thoughts about that.

[NeQuissimus]

I think keeping the implicit conversions behind an import will keep the compile times down for users. I would rather not expose them automatically.

What if we just create a syntax package in the core module?

We can then turn the string interpolation part into refined-contextual.