move lists of big and small words into module constants
compose is_big_word? method
add examples for subsidiary methods in String
add String#is_small_word? and examples

fix has_caps? method
change example word to something longer
replace opaque variable names with more descriptive names
add unicode versions of upcase, downcase, upcase! and downcase!

unicode_upcase, unicode_downcase, unicode_upcase! and unicode_downcase!
add examples
refactor to make use of these