Feature request: add -version flag

[vmarkovtsev]

sourced@sourced-MacBookPro:/tmp/enry$ /home/sourced/Projects/ast2vec/enry -version
flag provided but not defined: -version
 /home/sourced/Projects/ast2vec/enry v1.4.0 build: 09-07-2017_08_55_33 commit: 0fe0a97f67, based on linguist commit: 37979b2
 /home/sourced/Projects/ast2vec/enry, A simple (and faster) implementation of github/linguist
 usage: /home/sourced/Projects/ast2vec/enry <path>
        /home/sourced/Projects/ast2vec/enry [-json] [-breakdown] <path>
        /home/sourced/Projects/ast2vec/enry [-json] [-breakdown]

flag provided but not defined: -version

Update: I thought that there was such flag defined (the version was printed) but I was wrong. Thus I propose to add -version to print the version.