Optimize build speed by 97% or more

[Toflar]

Hi there!

My colleague informed me that building the phar file takes about 4 minutes. I couldn't believe this so I quickly looked into what the issue was. Blackfire told me 97% of all the time is needed at Phar::addFromString(). So I thought why not just write it all to a temporary directory, make it "lazy" and then add all of the files to the phar file at once using Phar::buildFromDirectory(). Turns out this works just fine for me and build time went down from 4 min 5 s to 7.05 s 😎

I couldn't add tests because the supported php versions and the used phpunit is so old that I sort of cannot get it to work without some serious changes. Do you plan to update the tests on master and update to a decent phpunit version? If so, I'll be happy to add tests for this stuff here.

Hope to help :-)

PS: Blackfire comparison: https://blackfire.io/profiles/compare/2d79d513-2460-4010-a797-914ba7237a7f/graph