Define syntax markers for automated linting tools

[mlange05]

Following on form the suggested general classification of subroutines in issue #5, I propose to add a rule for specific syntax markers that classify a subroutine or source file to adhere to a specific subset of rules (eg. the proposed "parallel" and "vector" routines). The markers would be intended for automated tools across organisations to verify if individual files adhere to the standard.

Explicit in-source marking would allow two things:

• Gradual implementation of the rules without relying on implicit inclusion and long lists of exception clauses. Once a rule has been tagged explicitly, it is assumed to be compliant with the defined subset of rules (effectively an "opt-in" mechanism).
• Complete adherence to the respective structural rules can be seen as a "contractual requirement" for automated GPU-adaptation. If all subroutines transitively called from a "parallel"/"driver" routine adhere to the "vector"/"NPROMA" rules, source-to-source tools should be able to automatically generate correct GPU-code for that code region.

My proposed format would be !$IAL-FORMAT: PARALLEL or !$IAL-FORMAT: VECTOR

Optionally we could also add exemption clauses that could be discussed on a file-by-file basis, eg.:
!$IAL-FORMAT: VECTOR, EXCEPT: L18