Fix dropping newlines, breaking some code blocks (#450)

Turns out that codeblocks, while usually being formatted as one text event containing all the lines, sometimes have multiple text events, each ending with a newline. When removing those newlines, they are (a) missing in the output, and (b) pulldown-cmark-to-cmark chokes on the indent of the end of codeblock (Byron/pulldown-cmark-to-cmark#69).

Fixes #440

src/output.rs

@@ -310,13 +310,16 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for EventFilter<'a, I> {
 				}),
 
 				Event::Text(text) if self.in_code_block => {
-					let filtered = text
+					let mut filtered = text
 						.lines()
 						.filter(|line| !is_hidden_codeblock_line(line))
 						.join("\n");
 					if filtered.is_empty() {
 						continue;
 					}
+					if text.ends_with('\n') {
+						filtered.push('\n');
+					}
 					Event::Text(filtered.into())
 				},
 

tests/pass/code-block-in-list/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "code_block_in_list"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[lib]
+path = "lib.rs"

tests/pass/code-block-in-list/README.j2

@@ -0,0 +1 @@
+{{readme}}

tests/pass/code-block-in-list/README.md

@@ -0,0 +1,13 @@
+This is an example testing code blocks in lists
+
+* in the past, this has caused issues
+
+* one of such cases was [\#440][__link0]
+
+* therefore, we have this example/test:
+
+  ```rust
+  struct Foo {
+      bar: usize
+  }
+  ```

tests/pass/code-block-in-list/lib.rs

@@ -0,0 +1,12 @@
+//! This is an example testing code blocks in lists
+//!
+//!   - in the past, this has caused issues
+//!   - one of such cases was [#440](https://github.com/msrd0/cargo-doc2readme/issues/440)
+//!   - therefore, we have this example/test:
+//!     
+//!     ```rust
+//!     # #[derive(Clone, Copy)]
+//!     struct Foo {
+//!         bar: usize
+//!     }
+//!     ```