Optionally hijacks -h/--help options

[nkakouros]

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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 771f9c2086c7aebfc829c7d255bc38c907c28dc2 on nkakouros-forks:help-hijack into 292e0803074eb538ab8633a657c53d3a975ba922 on mbland:master.