Bug 43104: Don't eat exclamation marks in table heading attribute names

Fixes bug 43104 (about https://en.wikipedia.org/wiki/Buri_Ram_Airport) by
making attribute name productions slightly less greedy.

Minimal test case:

echo -e '{|\n! Foo !! style="color: red" | Bar\n|}' | nodejs parse

No changes in parser tests, TODO: add test case above as test.

Change-Id: I0306390e037dc0b8b913bd61c7887a3c3a5034dd
Merge "Bug 43104: Don't eat exclamation marks in table heading attribute names"