add views

add views directory
add index.erb file
move text to display from get / to here
compose rot13 processing steps into private method
compose fmpxml display steps into private method
add sinatra-formhelpers-ng gem
allow input of string using a form

use sinatra-formhelpers-ng to add form to index.erb
change get method to post
no need to explicitly grab passed parameter - it's in the hash
already