Use Ructe (#327)

All the template are now compiled at compile-time with the `ructe` crate.

I preferred to use it instead of askama because it allows more complex Rust expressions, where askama only supports a small subset of expressions and doesn't allow them everywhere (for instance, `{{ macro!() | filter }}` would result in a parsing error).

The diff is quite huge, but there is normally no changes in functionality.

Fixes #161 and unblocks #110 and #273

.gitignore

@@ -1,4 +1,3 @@
-
 rls
 /target
 **/*.rs.bk
@@ -14,4 +13,6 @@ docker-compose.yml
 *.sqlite
 *.sqlite3
 *.swp
+tags.*
+!tags.rs
 search_index