updated description of anagrams exercise (#1928)

* updated description of anagrams

* changed anagram description to be one-sentence-per-line

* updated description of anagrams to use sets

Author: BartMassey

exercises/anagram/description.md

@@ -1,8 +1,13 @@
 # Description
 
-An anagram is a rearrangement of letters to form a new word.
-Given a word and a list of candidates, select the sublist of anagrams of the given word.
+An anagram is a rearrangement of letters to form a new word: for example `"owns"` is an anagram of `"snow"`.
+A word is not its own anagram: for example, `"stop"` is not an anagram of `"stop"`.
 
-Given `"listen"` and a list of candidates like `"enlists" "google"
-"inlets" "banana"` the program should return a list containing
-`"inlets"`.
+Given a target word and a set of candidate words, this exercise requests the anagram set: the subset of the candidates that are anagrams of the target.
+
+The target and candidates are words of one or more ASCII alphabetic characters (`A`-`Z` and `a`-`z`).
+Lowercase and uppercase characters are equivalent: for example, `"PoTS"` is an anagram of `"sTOp"`, but `StoP` is not an anagram of `sTOp`.
+The anagram set is the subset of the candidate set that are anagrams of the target (in any order).
+Words in the anagram set should have the same letter case as in the candidate set.
+
+Given the target `"stone"` and candidates `"stone"`, `"tones"`, `"banana"`, `"tons"`, `"notes"`, `"Seton"`, the anagram set is `"tones"`, `"notes"`, `"Seton"`.