change: quote default literatureNoteContentTemplate

[eddieantonio]

The default value of literatureNoteContentTemplate will generate YAML front matter that is often broken by special YAML characters. For instance, a colon (:) in the {{title}} will cause a syntax error in YAML. This adds quotes around both {{title}} and {{authorString}} in an attempt to remedy the easily-broken default.

For example, I created a literature note which contains a colon in the title. This is the result using the previous default template:

---
title: Ontology development 101: A guide to creating your first ontology
authors: Natalya F. Noy, Deborah L. McGuinness
year: 2001
---

(try this snippet in YAML Lint!)

Obsidian presents this as "Metadata (invalid YAML)" in the preview:

After the change, the front matter is as follows:

---
title: "Ontology development 101: A guide to creating your first ontology"
authors: "Natalya F. Noy, Deborah L. McGuinness"
year: 2001
---

After this change, the default is no longer broken by the titles containing colons or other YAML syntax.

Note: this may be considered a breaking change, as it changes the defaults of the plugin.

Fixes #117
Addresses #89