Add Percent Notation as a ruby til.

ruby/percent-notation.md

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+# Percent Notation
+
+Ruby has many uses for the `%` character. One of the more obscure uses is as
+a notion for custom delimited strings. Use the percent notation with a
+non-alphanumeric character to surround a string.
+
+```ruby
+> %=Jurassic Park=
+=> "Jurassic Park"
+> % Ghostbusters  
+=> "Ghostbusters"
+```
+
+It even works with balanced characters
+
+> %(The Goonies)
+=> "The Goonies"
+
+This is useful for defining a string that has both types of quotes
+
+```ruby
+> %[That'll be the "day"]
+=> "That'll be the \"day\""
+```
+
+It's also useful for creating horribly obfuscated code
+
+```ruby
+> %=what===%?what?
+=> true
+```
+
+h/t [Josh Davey](https://twitter.com/joshuadavey/status/615613617099046912)