added Mark Senn's solution to PWC 029 task 1 in Perl 6

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+#
+# Perl Weekly Challenge - 029
+# Task #1
+#
+# Mark Senn, http://engineering.purdue.edu/~mark
+# October 13, 2019
+#
+# From
+# https://perlweeklychallenge.org/blog/perl-weekly-challenge-029#task-1
+#     Write a script to demonstrate brace expansion.  For example,
+#     script would take command line argument
+#         Perl {Daily,Weekly,Monthly,Yearly} Challenge
+#     and should expand it and print like below:
+#         Perl Daily Challenge
+#         Perl Weekly Challenge
+#         Perl Monthly Challenge
+#         Perl Yearly Challenge
+#
+# ASIDE: HELP WANTED WITH PERL 6 CUSTOM SYNTAX
+#     This works:
+#         my @x = (<a b>, <c d>);
+#         @x.map({.join(':').say});
+#     I'd like for this to work so I don't need to type as much:
+#         @x.{.join(':').say};
+#     If you know how to do it please send me the answer at the email
+#     address in
+#         https://engineering.purdue.edu/~mark/
+#     Thank you.
+#
+# ASIDE: BASH SHELL HISTORY EXPANSION
+#     If you use ! followed by a command number to rerun that command
+#     or a string to rerun tha last command that started with that
+#     string and would like to change that to ',' because that is easier
+#     to type keep reading this ASIDE.
+#       I use ',' instead of '!' for my Bash shell history expansion
+#     character because I use shell history expansion often and ','
+#     is easier to type than '!'.  Because of that I'd need to type
+#         Perl {Daily\,Weekly\,Monthly\,Yearly} Challenge
+#     on the command line to do the challenge.  (I have things set
+#     up so that is the default input if no arguements are on the
+#     command line for this program, too.)
+#       From
+#     http://web.mit.edu/gnu/doc/html/features_4.html
+#         histchars
+#             Up to three characters which control history expansion,
+#             quick substitution, and tokenization (see section History
+#             Interaction). The first character is the
+#             history-expansion-char, that is, the character which
+#             signifies the start of a history expansion, normally
+#             `!'. The second character is the character which signifies
+#             `quick substitution' when seen as the first character on a
+#             line, normally `^'. The optional third character is the
+#             character which signifies the remainder of the line is a
+#             comment, when found as the first character of a word,
+#             usually `#'. The history comment character causes history
+#             substitution to be skipped for the remaining words on the
+#             line. It does not necessarily cause the shell parser to
+#             treat the rest of the line as a comment.
+#     To change my Bash shell history characters from '!^#' to ',^#'
+#     I put
+#         histchars=',^#'
+#     in my .bashrc file.  Other shells use histchars also---check
+#     the documentation for your shell if you are interested.
+#
+
+# Run using Perl v6.d;
+use v6.d;
+
+sub MAIN(*@arg);
+{
+    # If no command line arguments are given use these defaults.
+    # I couldn't figure out how to do this on the "sub MAIN" line
+    # without getting a "Cannot put default on slurpy parameter @arg"
+    # error.
+    (@arg.elems)
+        or  @arg = 'Perl', '{Daily,Weekly,Monthly,Yearly}', 'Challenge';
+
+    # Convert the @arg array to a @term array.  The next paragraph
+    # explains this in detail.
+    my @term = ();
+    for @arg  {
+        # If $_ starts with '{' and ends with '}' 
+        # set $0 to what's between the braces.
+        if  /^^ \{ (.*?) \} $$/  {
+            # Split $0 on commas and push the that array
+            # on @term as a single element.
+            push @term, $0.split(',');
+        }  else  {
+            # Push the scalar $_ on @term.
+            push @term, $_;
+        }
+    }
+
+    # At this point, if no command line arguments are set
+    #     $term[0]  is  'Perl'
+    #     $term[1]  is  ('Daily', 'Weekly', 'Monthly', 'Yearly')
+    #     $term[2]  is  'Challenge'
+    # $term[0] X $term[1] X @term[2] would give
+    #     ('Perl', 'Daily',   'Challenge')
+    #     ('Perl', 'Weekly',  'Challenge')
+    #     ('Perl', 'Monthly', 'Challenge')
+    #     ('Perl', 'Yearly',  'Challenge')
+    # If the program is called with a different number of
+    # arguments there will be a different number of @term
+    # elements set.  The reduction operator '[X]' puts a 'X'
+    # between each element of @term.  After the '([X] @term).'
+    # any of the following can be used to do what we want:
+    #     # Convert * to type Str and print it.
+    #     map(*.Str.say);
+    #     # Convert * to type Stringy and print it.
+    #     map(*.Stringy.say);
+    #     # Convert * to string and print it.
+    #     map((~*).say);
+    #     # Put a space between each element of $_ and print it.
+    #     map({join(' ',$_).say});
+    #     # Put a space between each element of $_ and print it.
+    #     map({$_.join(' ').say});
+    #     # Put a space between each element of $_ and print it.
+    #     # If a method is going to operate on $_ you don't need to
+    #     # specify '$_'.
+    #     map({.join(' ').say});
+    # I like the following line the best.
+    ([X] @term).map({.join(' ').say});
+}