New expression language docs!

We have updated the page for the Hail expression language documentation. It is now divided into 4 sections:

  • Language constructs (if...else, let...in)
  • Operators (a + b)
  • Types (Genotype, Variant, Int, Aggregable, Array[Int], …)
  • Functions (exp(x), fet(x), isDefined(x), …)