Feature request: rename output directive

[cxj]

PHP's Phar class sadly requires that the output file name's extension must be .phar. Hence, the output directive for box2 will always need to be named *.phar. However, I always like to rename my executable Phar archives to just the basename. I use composer not composer.phar, and box build not box.phar build, etc. Clearly I can rename my output many different ways (command line, Makefile, Composer script, etc.), but I'd really love to have a self-contained process where box can rename myapp.phar to myapp before exiting.

[JayBizzle]

Yes, also would like this!