Optionally hijacks -h/--help options

[nkakouros]

• I have reviewed the contributor guidelines.
• I have reviewed the code of conduct.
• Per GitHub's Terms of Service, I am aware that I license my
  contribution under the same terms as this project's license, and
  that I have the right to license my contribution under those terms.

cc: @mbland

Generally, it is a good practice to have -h, --help or -help print the help for a command. Right now, it is required that every new command that the users create to implement this. This PR adds a flag to enable go-core.bash to hijack these options and print the command help whenever they are present.

[coveralls]

Coverage increased (+0.04%) to 95.032% when pulling 771f9c2 on nkakouros-forks:help-hijack into 292e080 on mbland:master.