add user guide documents about project.
add and modify some sentences according to feedbacks.
make yobi.Markdown to global object

- typeof yobi.Markdown has changed to object from function
- RegExps are assigned to variables for performance improvement
update timeline partially on issueView (#392)
update timeline periodically(1m) on issueView
rename ambiguous method name, add renderMarkdown()

- renamed .render to .enableMarkdown()
- distinguish static value/function from _renderMarkdown()
  and set it as public method .renderMarkdown()
commentwrap:fixed icon of temp file on comment
pullrequest: updated merging commit message
DOCS: add code review user manual.
DOCS: modify items of TOC.
Markdown: move RegExp. value definitions into hook
pull-request-comment: fixes commitComment sorting
remove meaningless implicit lang parameters
notification: save receivers explicitly
pullrequest: refactoring merge message
Merge pull request #244 from whiteship/yobi refs/heads/pullreuqest/merge
Merge pull request #227 from changsung/yobi refs/heads/userManual-project
Merge pull request #240 from insanehong/hive refs/heads/issue/tmp-file-icon
email: fixed to login after validation
Merge pull request #257 from whiteship/yobi refs/heads/user/email