Fix test_double_quoted_strings_are_strings

* in about_strings.rb

[#54145639]
Fix test_single_quoted_strings_are_also_strings

* in about_strings.rb

[#54145639]
Fix about_strings.rb

* Use single quotes to create string with double
  quotes

[#54145639]
Fix about_strings.rb

* Use double quotes to create string with single
  quotes

[#54145639]
Fix about_strings.rb

* test_use_backslash_for_those_hard_cases

[#54145639]
Fix about_strings.rb

* Flexible quotes use %(), %!!, or %{}

[#54145639]
Fix about_strings.rb

* Flexible quotes can handle multiple lines

* string responds to .length, .lines .count

* "\n" == new line in a string

[#54145639]
Fix about_strings.rb

* <<EOS EOS handles multiple lines also

[#54145639]
Fix about_strings.rb

* + will concatenate two strings

[#54145639]
Fix about_strings.rb

* Concatenation with + leaves original strings
  unmodified

[#54145639]
Fix about_strings.rb

* += concatenates to the end of a string

[#54145639]
Fix about_strings.rb

* += will concatenate and change the string.

* test title doesn't make any sense!

[#54145639]
Fix about_strings.rb

* Shovel operator is <<

* Appends content to a string.

[#54145639]
Fix about_strings.rb

* Shovel operator does append to the original 
  string, even through associations.  Weird!

[#54145639]
Fix about_strings.rb

* "\n" escaped chars.size = 1 ! 2

* "" interpret the characters escaped by \

[#54145639]
Fix about_strings.rb

* '\n' do not escape chars, .size reads as 2

[#54145639]
Fix about_strings.rb

* single quotes sometimes interpret escape
  characters

* '\\\'' .size = 2 && "\\'"

[#54145639]
Fix about_strings.rb

* #{} interpolates values in a string, useful
  for variables, etc.

[#54145639]
Fix about_strings.rb

* #{} does not work with single quotes 

[#54145639]
Fix about_strings.rb

* #{} allows any Ruby expression to be 
  interpolated

* i.e. math, string methods, etc.

[#54145639]