modify art page to display thumbnails

thumbnails are currently created using shell script and require
imagemagick installed on the server. i know it's stupid, but i think
that including thumbnails to repo is also stupid.

maybe later i replace this script with actual jekyll plugin, but for
this i'll need to familiarize myself with ruby.
but now i use following addition to the git hook on the server:

```
[ -f "$TMP_GIT_CLONE/art/thumbs.sh" ] && {
    dir="$PWD"
    cd "$TMP_GIT_CLONE/art/" && sh thumbs.sh && cd "$dir"
}
```

it happens after cloning to remote repo and before building with bundle.

overall, this is a bodge now, it recompiles all thumbnails every time
due to quirks in my current setup.

1 files changed, 7 insertions, 0 deletions

diff --git a/_config.yml b/_config.yml
index a74072f..1f827a6 100644
--- a/_config.yml
+++ b/_config.yml
@@ -7,6 +7,7 @@ plugins:
 exclude:
   - LICENSE
   - README.md
+  - art/thumbs.sh
 
 excerpt_separator: <!--more-->
 
@@ -30,3 +31,9 @@ defaults:
       path: "art"
     values:
       art: true
+
+  - scope:
+      path: "art/*/thumbs"
+    values:
+      thumbnail: true
+