resurect Phar building code removed in 8483fb709b2285a033515f59b4ad818468a0372a

changes:

* make WP_CLI_ROOT relative to the root dir, not to php/
* remove man/ and add vendor/rmmcue
add symfony/finder as dev dependency
run the functional tests against the Phar file
phar: add missing rumsaa/array_column dependency
phar: add all files from the templates/ directory
give shorter names to ci scripts
move WP_CLI_BIN_DIR env variable to .travis.yml
move Phar building to ci/prepare.sh and rename ci/build.sh to ci/test.sh
automatically deploy Phar file to wp-cli/builds
Merge pull request #658 from wp-cli/phar-builder

Bring back Phar archives