allow "acbuild script" read from stdin

[dimas]

I believe it is a convention that tools that accept file names can be given "-" to indicate stdin so "cat -" is the same as just "cat" (because for cat, stdin is the default source) but the fact is you can specify it explicitly.

Right now "acbuild script -" complains that it cannot find file "-".

Supporting stdin would allow use here-doc / here-text notations and embed ACB scripts into shell scripts

acbuild --debug script - <<END_TEXT

copy $SRC /temp
run -- bash /temp/something.sh
run -- rm -rf /temp

END_TEXT

[koflerdavid]

Reading from /dev/stdin worked for me. Of course, having a flag would be nicer.