Fix a number of discovered typos, capitalization of developer and

doc/api/issues.md

doc/api/oauth2.md

doc/api/projects.md

doc/api/services.md

doc/development/architecture.md

doc/development/ci_setup.md

doc/install/requirements.md

doc/integration/README.md

doc/integration/external-issue-tracker.md

doc/integration/gitlab_buttons_in_gmail.md

doc/integration/shibboleth.md

doc/markdown/markdown.md

doc/project_services/project_services.md

doc/raketasks/backup_restore.md

doc/release/howto_rc1.md

doc/release/monthly.md

doc/security/information_exclusivity.md

doc/system_hooks/system_hooks.md

doc/update/2.6-to-3.0.md

doc/update/4.2-to-5.0.md