Fix line endings and add a .gitattributes file.

The .gitattributes file can be used to enforce and manage the types of line
endings desired for specific types of files at the repository, as well as
to manage GitHub's automatic detection of documentation and the types of
programming languages used at the repository.

I've commented links to the relevant documentation within the attached
.gitattributes file to assist with guiding future additions to the file.

.gitattributes

@@ -0,0 +1,18 @@
+# AVideo .gitattributes file.
+
+# Refer to:
+# https://help.github.com/articles/dealing-with-line-endings/
+
+*.yaml eol=lf
+*.yml eol=lf
+
+# Refer to:
+# https://github.com/github/linguist
+
+*.md linguist-documentation
+*.txt linguist-documentation
+
+.github/* -linguist-detectable
+.vscode/* -linguist-detectable
+node_modules/* -linguist-detectable
+vendor/* -linguist-detectable