test for bug fix : worksheet/test_write_formula_does_not_change_formula_string.rb
bug fix : test_write_formula_does_not_change_formula_string.rb PASS!
test add : test_outline_collapesd in test_example_match.rb
examples/outline_collapsed.rb added.
Merge branch 'bug_fix_in_write_formula'
README.rdoc : add comment about bug fix in write_formula