add backup of slide in PDF format

- cohama's slide are missing
- thinca's slide is markdown
Add cohama's slide
Update supermomonga's slide
Remove Linda_pp's one :dog:
Rename slide/ to slides/
Merge remote-tracking branch 'origin/gh-pages' into pr/52
show DL (download) link in "reports" page
Merge branch 'pr/52' into gh-pages