Add a test case showing only paragraphs exist on the first line for plain lists.

org_mode_samples/plain_lists/start_nested_list_same_line.README.txt

@@ -0,0 +1 @@
+Seems like the only element that can exist on the same line as the opening of an item is a paragraph. Perhaps all other elements should have a start of line matcher at the beginning of their parser to force this?

org_mode_samples/plain_lists/start_nested_list_same_line.org

@@ -0,0 +1,4 @@
+1. regular
+   1. nested list
+2. 1. Sameline
+3. | table|

src/parser/plain_list.rs

@@ -1 +1,11 @@
+use super::error::Res;
+use super::lesser_element::Paragraph;
+use super::Context;
 
+#[allow(dead_code)]
+pub fn plain_list_item<'r, 's>(
+    context: Context<'r, 's>,
+    input: &'s str,
+) -> Res<&'s str, Paragraph<'s>> {
+    todo!()
+}