#181 Add version information calls C4Version() and C4VersionDetails()

[kirchsth]

Implementation of #181 with the version "2.3.1beta1" (it could be that in the next 5 days version 2.3.2beta1 is displayed, but this is related to the caching problem of the PlantUML online server)

Version information

Starting with v.2.3.1beta1 C4-PlantUML offers version information like PlantUML with its %version() call.

• C4Version(): Current C4-PlantUML version (e.g. "2.3.1beta1").
• C4VersionDetails(): (Floating) version details with the current PlantUML and C4-PlantUML version (with the alias C4VersionDetailsArea)

@startuml
' unitil merge is finished my extended branch is used in sample
' !include https://raw.githubusercontent.com/kirchsth/C4-PlantUML/extended/C4_Container.puml
!include https://raw.githubusercontent.com/kirchsth/C4-PlantUML/extended/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