Don't require blank line before markdown lists

Fixes #11249 to follow the CommonMark spec for lists which does not
require a blank line prior to the start of a list.

base/markdown/Common/block.jl

@@ -263,6 +263,7 @@ isordered(list::List) = list.ordered >= 0
 const BULLETS = r"^ {0,3}(\*|\+|-)( |$)"
 const NUM_OR_BULLETS = r"^ {0,3}(\*|\+|-|\d+(\.|\)))( |$)"
 
+@breaking true ->
 function list(stream::IO, block::MD)
  withstream(stream) do
  bullet = startswith(stream, NUM_OR_BULLETS; eat = false)

test/markdown.jl

@@ -166,6 +166,33 @@ let doc = md"""
  @test doc.content[2].items[3][1].content[1] == "zombie"
 end
 
+let doc = Markdown.parse(
+ """
+ A paragraph...
+ - one
+ - two
+ * three
+ * four
+ ... another paragraph.
+ """
+ )
+
+ @test length(doc.content) === 3
+ @test isa(doc.content[1], Markdown.Paragraph)
+ @test isa(doc.content[2], Markdown.List)
+ @test isa(doc.content[3], Markdown.Paragraph)
+
+ @test length(doc.content[2].items) === 2
+ @test doc.content[2].items[1][1].content[1] == "one"
+ @test length(doc.content[2].items[2]) == 2
+ @test doc.content[2].items[2][1].content[1] == "two"
+
+ @test isa(doc.content[2].items[2][2], Markdown.List)
+ @test length(doc.content[2].items[2][2].items) === 2
+ @test doc.content[2].items[2][2].items[1][1].content[1] == "three"
+ @test doc.content[2].items[2][2].items[2][1].content[1] == "four"
+end
+
 @test md"Foo [bar]" == MD(Paragraph("Foo [bar]"))
 @test md"Foo [bar](baz)" != MD(Paragraph("Foo [bar](baz)"))
 @test md"Foo \[bar](baz)" == MD(Paragraph("Foo [bar](baz)"))