feat: new HL7_2_7()

[Bugs5382]

Class System for Each Spec which would allow the user not have to know the "values" that they need or could enter.

I envision this as:

const hl7 = new HL7_2_7(); 
hl7.produceMSH( { ....MSH } )
hl7.produceEVN( { ...EVN } )
/// etc.. would build out the full HL7 Message with strong-typescript, checked inputs.

This would be different from the Message//FileBatch//Batch classes where they are more generic, the classes for each spec would confirm to what it can produce. For example 2.1 has limited specs in terms of different segments allowed. The Message class would help in this case and the overall HL7_2_7 would return a Message object. This way it can be added to the Batch or FileBath functions.

Some functions inside the overarching might not exist. For example AL1 segment does not exist on 2.1 but does in 2.2.

For now for milestone 1.0.0, we are just trying to get something out the door :)

[Bugs5382]

GitHub's Octokit is a good example of how this should be 'dynamic' and 'conditional'.