Add tasks for all the new languages

Task/Binary-strings/Nim/binary-strings.nim

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+var # creation
+  x = "this is a string"
+  y = "this is another string"
+  z = "this is a string"
+
+if x == z: echo "x is z" # comparison
+
+z = "now this is another string too" # assignment
+
+y = z # copying
+
+if x.len == 0: echo "empty" # check if empty
+
+x.add('!') # append a byte
+
+echo x[5..8] # substring
+echo x[8 .. -1] # substring
+
+z = x & y # join strings
+
+import strutils
+
+echo z.replace('t', 'T') # replace occurences of t with T