Updated style of Hash#default_proc spec, added more cases
Updated style of Hash#dup spec
Updated style of Hash#delete spec
Updated style of Hash#each spec, added more cases
Updated style of Hash#each_with_index spec, added tests
Updated style for Hash#empty? spec, added spec for Hash.empty
Updated style of Hash#== and #eql? specs, added another test
Updated style of Hash#except spec, added a test
Hash, Vector, and SortedSet #fetch prefers default block to default arg

This is to match the behavior of built-in Ruby Hash#fetch.