Read target from stdin

[inshua]

Is your feature request related to a problem? Please describe.
An important feature.

Describe the solution you'd like
No way, I need create a temporary file and delete it

Describe alternatives you've considered

echo 'hello world' | yara a_rule.yar
echo '5A 4D ...' | yara --hex pe_rule.yar

It will be very nice for test whether a rule works.

Additional context
(none)