Merge pull request #15 from Kunstmaan/develop

merge develop to master (adds slider)
Merge pull request #17 from Kunstmaan/develop

merge develop into master (adds full img bg fix)
Merge pull request #18 from Kunstmaan/develop

Update full-img-bg.md
fix if null
Merge pull request #19 from Kunstmaan/fix/full_img_bg_if_null_check

fix if null