Muse reader: incorrect handling of "**" between words

[link2xt]

**Foo bar**bat baz** produces

<p>*<em>Foo barbat baz</em>*</p>

but should produce

<p><strong>Foo bar**bat baz</strong></p>

instead.

Text::Amuse is correct here.

Related: Alhadis/language-emacs-lisp#5

[link2xt]

Partially addressed in 13e0ac1

[link2xt]

This one is more problematic, because * preceded by * is parsed as the start of normal emphasis:

$ pandoc -f muse -t html
**foo*
^D
<p>*<em>foo</em></p>

This makes it impossible to parse closing ** in **Foo bar**bat baz** as the first asterisk is consumed by emphasis.

This should be parsed as plain text: **foo*.