Add version subcommand to the CLI. Fixes #184

[cvhariharan]

This PR adds a version subcommand which has a default value of development for both CLI and Genji. It automatically picks up the tag during CI.

Example output for genji version

Genji 1.0.0
Genji CLI 1.0.0

If tag is not set / empty,

Genji development
Genji CLI development

[codecov-io]

Codecov Report

Merging #254 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #254   +/-   ##
=======================================
  Coverage   61.35%   61.35%           
=======================================
  Files          68       68           
  Lines        6345     6345           
=======================================
  Hits         3893     3893           
  Misses       1936     1936           
  Partials      516      516           

Impacted Files	Coverage Δ
db.go	45.00% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ca94a13...4950f61. Read the comment docs.

[asdine]

Thanks!