Scan all descending directories for index.js with 'create index';

[gajus]

Instead of requiring user to pass all directories, have an option that enables deep scanning of the directory tree of files containing 'create index'; directive and automatically update those indexes, e.g.

create-index --deep ./src

The latter would be equivalent to ./src/**/index.js being searching for files with 'create index';, updating their index and ignoring other directories.