Add a .gitattributes file to specify eol=LF (#1370)

* Add a .gitattributes file specifying LF-style line endings.

This is similar to [Rust's .gitattributes file] though simplified.
Most of our source and documentation files already used LF-style line
endings, including *.cs files, so this makes things more consistent.

[Rust's .gitattributes file]: https://github.com/rust-lang/rust/blob/master/.gitattributes

* Remove UTF-8 BOMs in *.cs files.

Most of our *.cs files don't have UTF-8 BOMs, so this makes things more
consistent.

crates/misc/dotnet/docs/toc.yml

@@ -1,7 +1,7 @@
-- name: Articles
-  href: articles/
-- name: API Documentation
-  href: api/
-  homepage: api/index.md
-- name: GitHub Repo
-  href: https://github.com/bytecodealliance/wasmtime
+- name: Articles
+  href: articles/
+- name: API Documentation
+  href: api/
+  homepage: api/index.md
+- name: GitHub Repo
+  href: https://github.com/bytecodealliance/wasmtime