teximg: Make TeX handle preventing unsafe things; remove insufficient blacklist
TeX has configuration options that prevent unsafe things like shell
escapes and insecure file reads/writes. Turn all of them on.
teximg's regex-based blacklist does not suffice. For instance:
[[!teximg code="""
\catcode`\%=0
%input{/etc/passwd}
"""]]
Remove the blacklist, since the TeX configuration options seal off the
underlying mechanisms more safely, and the blacklist blocks other TeX
commands that can prove useful.