Add tasks for all the new languages

Task/Substring-Top-and-tail/Sidef/substring-top-and-tail-1.sidef

@@ -0,0 +1,4 @@
+say "knight".substr(1);       # strip first character
+say "socks".substr(0, -1);    # strip last character
+say "brooms".substr(1, -1);   # strip both first and last characters
+say "与今令".substr(1, -1);    # => 今

Task/Substring-Top-and-tail/Sidef/substring-top-and-tail-2.sidef

@@ -0,0 +1,4 @@
+var gstr = "J\x{332}o\x{332}s\x{332}e\x{301}\x{332}";
+say gstr-/^\X/;                    # strip first grapheme
+say gstr-/\X\z/;                   # strip last grapheme
+say gstr.sub(/^\X/).sub(/\X\z/);   # strip both first and last graphemes