HL7.get/2 is missing a return type

[gabbybene]

HL7.get/2 can return a list of hl7_map_data() when selecting multiple segments, but this is currently missing from the function's typespec.

Example:

import HL7
HL7.Examples.wikipedia_sample_hl7()
|> HL7.new!()
|> HL7.get(~p"OBX[*]")

returns

[
  %{
    0 => "OBX",
    1 => "1",
    2 => %{1 => %{1 => "N", 2 => %{1 => "K", 2 => "M"}}},
    3 => %{1 => %{2 => "Body Height"}},
    5 => "1.80",
    6 => %{1 => %{1 => "m", 2 => "Meter", 3 => "ISO+"}},
    11 => "F"
  },
  %{
    0 => "OBX",
    1 => "2",
    2 => "NM",
    3 => %{1 => %{2 => "Body Weight"}},
    5 => "79",
    6 => %{1 => %{1 => "kg", 2 => "Kilogram", 3 => "ISO+"}},
    11 => "F"
  }
]