Adds splat/2 to HL7 API

[Chase-Callahan]

Resolves #75

Description of Work

Extends the HL7 API to allow for bulk updates of paths on a parsed_hl7 data structure. This is a convenience function that will allow consumers to either statically or dynamically bulk update HL7 messages.

Testing instructions

1. Start iex session iex -S mix
2. Attempt to execute splat and extract value

import HL7

hl7 = HL7.Examples.wikipedia_sample_hl7() |> HL7.new!()

splat(hl7, %{~p"PID-99" => "FOO"}) |> get(~p"PID-99")