Support substitution

[luyui]

Should workaround #164 #783 #1699 etc.
Requires a manual creation of:

$ ln -s /proc/self/fd /dev/fd

[kalebmckale]

Did this get merged?

[e-maryniak]

Any idea when this will get merged?

Just as a side note: bash does not run, by default, in Posix mode.
Posix mode does not support bash's process substitution "cmd <( ... )".
You can check this with 'set -o' (it should list "posix off").
But indeed iSH is not running in Posix mode, so that did not explain why process substitution did not work.
So please accept this merge request, as I'm using process substitution frequently in my bash scripts!