Add tomland and validation-selective

[telser]

Happy to split this into two if that is preferred.

Checklist for adding a package:

• Meaningful commit message, eg add my-cool-package (please don't mention the yaml file)

• Package is already added to nightly (if possible)

• On your machine, in a new directory, you have successfully run the following set of commands (replacing $package and $version with the name and version of the package you want to add to Stackage LTS):

  stack unpack $package-$version
  cd $package-$version
  stack init --resolver lts
  stack --resolver lts build --haddock --test --bench --no-run-benchmarks
  

or using the verify-package script:

  verify-package $package lts

[alexeyzab]

Thanks!