New doc topic: issues

doc/README.md

doc/gitlab-basics/README.md

doc/gitlab-basics/create-issue.md

doc/intro/README.md

doc/user/project/issues/closing_issues.md

doc/user/project/issues/create_new_issue.md

doc/user/project/issues/crosslinking_issues.md

doc/user/project/issues/due_dates.md

doc/user/project/issues/img/button_close_issue.png

doc/user/project/issues/img/close_issue_from_board.gif

doc/user/project/issues/img/closing_and_related_issues.png

doc/user/project/issues/img/confidential_issues_create.png

...ser/project/issues/img/confidential_issues_index_page.png

...ser/project/issues/img/confidential_issues_issue_page.png

...r/project/issues/img/confidential_issues_search_guest.png

.../project/issues/img/confidential_issues_search_master.png

...r/project/issues/img/confidential_issues_system_notes.png

doc/user/project/issues/img/due_dates_create.png

doc/user/project/issues/img/due_dates_edit_sidebar.png

doc/user/project/issues/img/due_dates_issues_index_page.png