This commit fixes the base template lookup order to match the behaviour of regular templates.
```
1. <current-path>/<template-name>-baseof.<suffix>, e.g. list-baseof.<suffix>.
2. <current-path>/baseof.<suffix>
3. _default/<template-name>-baseof.<suffix>, e.g. list-baseof.<suffix>.
4. _default/baseof.<suffix>
For each of the steps above, it will first look in the project, then, if theme is set,
in the theme's layouts folder.
```
Fixes#2783
TOML and YAML handles integers differently, creating issues when using integer values from configuration or front matter in the First template function.
This currently works in YAML (parses into int), but not in TOML (parses into int64).
This commit modifies First so it accepts any int.
Fixes#551
The Intersect template-method would fail if one or both of the lists were nil (post vs page; post has tags, page has not).
This commit adds a nil-check and returns an empty result if any of the inputs are nil.
See #537
