Fix several problems caused by ill-formed documents.

The line number is not calculated correctly for DOS-style line breaks.

Fix error reporting in '''remove_possible_simple_key'''. The problem is caused by the document:

{{{
+foo: &A bar
+*A ]
}}}

Raise an error for a complex key which is not indented correctly, for instance:

{{{
? "foo"
 : "bar"
}}}
4 files changed