LaTeX reader: allow macro definitions inside macros.
Previously we went into an infinite loop with
```
\newcommand{\noop}[1]{#1}
\noop{\newcommand{\foo}[1]{#1}}
\foo{hi}
```
See #4253.
commitdca0032b0ebf99f374b3d8fc3942abfc3955de40
authorJohn MacFarlane <jgm@berkeley.edu>
dateSat 13 Jan 2018, 12:10 (9 years ago)
parent44222e0
test/command/4253.mdnew file+8
@@ -0,0 +1,8 @@
1+```
2+% pandoc -f latex -t native
3+\newcommand{\noop}[1]{#1}
4+\noop{\newcommand{\foo}[1]{#1}}
5+\foo{hi}
6+^D
7+[Para [Str "hi"]]
8+```