Add C4Version() functions which displays the PlantUML version and C4-PlantUML version

[kirchsth]

Like the PlantUML '%version()' function a C4Version() a and C4VersionDetails() function should be added that the active C4-PlantUML version can be checked too.

Eg.

@startuml
!include <C4/C4_Container.puml>

' existing plantuml version as text
%version()

' new C4-Plantuml version as text 
C4Version()

' new C4-Plantuml version details (incl. PlantUML version) as table
C4VersionDetails()

' version functions used in e.g. footer
footer drawn with PlantUML v. %version() and C4-PlantUML v. C4Version()
@enduml

Image was drawn with

@startuml
!include <C4/C4_Container.puml>

' >>>>>>>>>>>>>>>> new functions
!function C4Version()
  !return "2.3.2beta1"
!end function

!procedure C4VersionDetails()
rectangle C4VersionDetailsArea <<legendArea>> [
| PlantUML | **%version()** |
| C4-PlantUML | **C4Version()** |
]
!end procedure
' new functions <<<<<<<<<<<<<<<<

' existing plantuml version as text
%version()

' new C4-Plantuml version as text 
C4Version()

' new C4-Plantuml version details (incl. PlantUML version) as table
C4VersionDetails()

' version functions used in e.g. footer
footer drawn with PlantUML v. %version() and C4-PlantUML v. C4Version()
@enduml