add explanation of concepts to various design.md documents

[mikedamay]

There is a mismatch (see tables, below) between the concepts attributed to an exercise in csharp/reference/README.md which reflects the original concept-scraping task performed by the track's maintainers and what is shown for each exercise in csharp/config.json which is the official catalog of completed exercises.

The task, here, is to align the concepts associated in an exercise in csharp/config.json with those in csharp/reference/exercises.json (from which csharp/reference/README.md is generated).

For each concept found in config.json, not in exercises.json

• check if the concept is fully illustrated or described in the exercise to which it is attributed
• if the concept is fully illustrated or described then:
  • add the concept's name and a brief description to the exercise's design.md document
  • add the concept to the exercise in csharp/reference/exercises.json.
• if the concept is not fully illustrated or described in the exercise but it is an appropriate concept for the exercise then:
  • amend the exercise's introduction.md, after.md and/or the code files and instructions to reflect the concept
  • add the concept's name and a brief description to the exercise's design.md document
  • add the concept to the exercise in csharp/reference/exercises.json.
• if the concept is not fully illustrated or described in the exercise and it is not an appropriate concept for the exercise then:
  • add the concept to the unallocated-concepts exercise at the end of exercises.json where it can be picked up for further review

For each concept found in exercises.json, not in config.json

• check if the concept is fully illustrated or described in the exercise to which it is attributed
• if the concept if fully illustrated or described then:
  • add the concept to the exercise in csharp/config.json.
• if the concept is not fully illustrated or described in the exercise but it is an appropriate concept for the exercise then:
  • amend the exercise's introduction.md, after.md and/or the code files and instructions to reflect the concept
  • add the concept to the exercise in csharp/config.json.
• if the concept is not fully illustrated or described in the exercise and it is not an appropriate concept for the exercise then:
  • take the concept from the exercise in exercises.json and move it to the unallocated-concepts exercise in exercises.json where it can be picked up for further review

Concepts in csharp/config.json not in csharp/reference/exercises.json

Exercise	Concept
flag-enums	compound-assignment
integral-numbers	casting
method-overloading	named-arguments

Concepts in csharp/reference/exercises.json not in csharp/config.json

Exercise	Concept
classes	encapsulation
classes	fields
classes	objects
classes	state
classes	visibility
classes	default-value
inheritance	polymorphism
basics	return-values
basics	mutation
basics	functions
basics	type-inference
basics	comments
basics	scoping
basics	variables
nullability	null-coalescing
nullability	null-conditional
nullability	null-forgiving
nullability	nullable-values
numbers	math-operators
numbers	assignment
dictionaries	base-class-library
equality	marker-interfaces
parameters	named-arguments
parameters	out-parameters
parameters	optional-arguments
time	cross-platform
interfaces	explicit-interfaces
integral-numbers	unsigned-integers
lists	collections
namespaces	imports
string-formatting	interpolation
casting	implicit-casting

[mikedamay]

Concepts in csharp/config.json not in csharp/reference/exercises.json addressed in PR exercism/v3#2260.

[mikedamay]

The missing concepts related to classes are discussed here

[mikedamay]

The missing concepts related to classes are addressed with PR exercism/v3#2822.

[mikedamay]

Included polymorphism as part of the inheritance concept - PR exercism/v3#2887

[mikedamay]

The issues related to the basics exercise/concept have been resolved in PR exercism/v3#3059. All the missing concepts are treated as sub-concepts of the basics concept.