remove docdiff, using rubygems version now.

# Please enter the commit message for your changes. Lines starting
# with '#' will be kept; you may remove them yourself if you want to.
# An empty message aborts the commit.
# On branch master
# Your branch is ahead of 'origin/master' by 1 commit.
#   (use "git push" to publish your local commits)
#
# Changes to be committed:
#   (use "git reset HEAD^1 <file>..." to unstage)
#
#	modified:   Gemfile
#	modified:   Gemfile.lock
#	deleted:    hiki/docdiff/charstring.rb
#	deleted:    hiki/docdiff/diff.rb
#	deleted:    hiki/docdiff/diff/contours.rb
#	deleted:    hiki/docdiff/diff/editscript.rb
#	deleted:    hiki/docdiff/diff/rcsdiff.rb
#	deleted:    hiki/docdiff/diff/shortestpath.rb
#	deleted:    hiki/docdiff/diff/speculative.rb
#	deleted:    hiki/docdiff/diff/subsequence.rb
#	deleted:    hiki/docdiff/diff/unidiff.rb
#	deleted:    hiki/docdiff/difference.rb
#	deleted:    hiki/docdiff/document.rb
#	deleted:    hiki/docdiff/encoding/en_ascii.rb
#	deleted:    hiki/docdiff/encoding/ja_eucjp.rb
#	deleted:    hiki/docdiff/encoding/ja_sjis.rb
#	deleted:    hiki/docdiff/encoding/ja_utf8.rb
#	deleted:    hiki/docdiff/view.rb
#
remove hikidoc, using rubygems version now.
disabled fragile assertion
silent warning: circular dependency