Allow to set cache and content directories from environment
Summary: Per https://12factor.net/config
Test Plan:
$ setenv CACHE_DIR /var/cache/zed/zed51.dereckson.be $ setenv CONTENT_DIR /srv/zed/content $ php index.php […] $ ls /var/cache/zed/zed51.dereckson.be/sessions sess_11e39d475e41b9dc58a8b74d01f134d7 $ ls /var/cache/zed/zed51.dereckson.be/compiled 4bd4601ca5eedfb5f2a4f5d9c7a4e4e37f0dc838.core.conf.config.php f95e1e9dd1558a05ff237117ea19f5aaebcabcf0.file.login.tpl.php
Reviewers: dereckson
Reviewed By: dereckson
Differential Revision: https://code.zed.dereckson.be/D12