Parsing: Provide parseFromString'.

This is a verison of parseFromString specialied to
ParserState, which resets stateLastStrPos at the end.
This is almost always what we want.

This fixes a bug where `_hi_` wasn't treated as emphasis in
the following, because pandoc got confused about the
position of the last word:

    - [o] _hi_

Closes #3690.

1 files changed, 8 insertions, 0 deletions

diff --git a/test/command/3690.md b/test/command/3690.md
new file mode 100644
index 000000000..213b88138
--- /dev/null
+++ b/test/command/3690.md
@@ -0,0 +1,8 @@
+```
+% pandoc
+- [o] _hi_
+^D
+<ul>
+<li>[o] <em>hi</em></li>
+</ul>
+```