Extract WP_CLI_VERSION to a separate file

- Implements #680
- It is now possibile to set the version at build time (required for #1535): --version=x.y.z
- Keywords for incrementing the version number by one: --version=[patch|minor|major]
- When no arguments are passed, the old behaviour is preverved
- utils/update-phar takes an option argument: `update-phar [same|patch|minor|major|x.y.z]`
WP_CLI\Utils\increment_version() and tests
add a new line at the end of php/utils.php
Use WP_CLI\Configurator instead of Ulrichsg\Getopt\Getopt in utils/make-phar.php
Merge pull request #1539 from nyordanov/extract-version-info

Extract WP_CLI_VERSION to a separate file