Create tebako as a Ruby gem

[ronaldtse]

From #96 (comment)

The goal is to achieve:

$ gem install tebako
$ tebako press --root=packed-mn --entry-point=bin/metanorma --output=metanorma-package

$ tebako press \
  --root='~/projects/myproject' \
  --entry=start.rb \
  --output=/temp/myproject.tebako

[ronaldtse]

Things to be done:

• Move exe/package into lib/tebako/packager.rb.
• Move most code from exe/tebako into lib/tebako/cli.rb

[maxirmx]

Will do
Thank you, @ronaldtse