Add Ex 14 of LRTHW.

Add Exercise 14 of Learn Ruby the Hard Way. Reviews variable
interpolation in strings, use of STDIN with gets and chomp,
multiline strings.
Add mistakes in Ex 14 to mistakes list.

I forgot some lines of a program and it threw a fatal error.
Easy fix.
Confirm completion of Ex 14, EC 1 of LRTHW.

Confirm completion of Exercise 14, Extra Credit 1 of Learn Ruby the
Hard Way. Played Zork. It was okay.
Add Ex 14, EC 2 of LRTHW.

Add Exercise 14, Extra Credit 2 of Learn Ruby the Hard Way. This
exercise is a copy of Exercise 14 with the prompt changed.
Add Ex 14, EC 3 of LRTHW.

Add Exercise 14, Extra Credit 3 of Learn Ruby the Hard Way. Adds a
second argument to the script in Exercise 14. To accommodate this
change, I completely reworked the Exercise 14 script.
Add Ex 14, EC 4 of LRTHW.

Add Exercise 14, Extra Credit 4 of Learn Ruby the Hard Way. Made sure
I understood string interpolation inside multiline strings by taking
notes on the multiline string syntax. It turns out that the multiline
strings are "here documents".