Disallow link destination beginning with `<` unless it is inside `<..>`.

This brings the description in line with the spec example:

```
[foo]: <bar>(baz)

 [foo]
 .
 <p>[foo]: <bar>(baz)</p>
 <p>[foo]</p>
```

Closes #538.

1 files changed, 7 insertions, 6 deletions

diff --git a/spec.txt b/spec.txt
index a53e762..0bbd360 100644
--- a/spec.txt
+++ b/spec.txt
@@ -7338,12 +7338,13 @@ A [link destination](@) consists of either
   closing `>` that contains no line breaks or unescaped
   `<` or `>` characters, or
 
-- a nonempty sequence of characters that does not include
-  ASCII space or control characters, and includes parentheses
-  only if (a) they are backslash-escaped or (b) they are part of
-  a balanced pair of unescaped parentheses.  (Implementations
-  may impose limits on parentheses nesting to avoid performance
-  issues, but at least three levels of nesting should be supported.)
+- a nonempty sequence of characters that does not start with
+  `<`, does not include ASCII space or control characters, and
+  includes parentheses only if (a) they are backslash-escaped or
+  (b) they are part of a balanced pair of unescaped parentheses.
+  (Implementations may impose limits on parentheses nesting to
+  avoid performance issues, but at least three levels of nesting
+  should be supported.)
 
 A [link title](@)  consists of either