b3bp sourced mode

[mstreuhofer]

If main.sh is being sourced instead of being executed it respects the
variables __usage and __helptext being defined beforehand. Its behaviour
will depend on the sourcing script. If __usage is defined but empty no
argument parsing is done. If __helptext is defined but empty no helptext
will be shown.

Logging support still exists as it did before. The environment variables
LOG_LEVEL and NO_COLOR are supported just as they were before.

[mstreuhofer]

This "sourced mode" does not change any behaviour of the script main.sh as it
was before -- as long as __usage is not already defined before main.sh being
sourced. This should cover all supported (documented) cases of downstream
usage.

The new script example.sh shows how b3bp can be used by downloading and
directly sourcing it without having to change anything, yet get the benefits of
getopts parsing, help and logging.

If main.sh is executed it behaves exactly as before. If it is sourced but no
__usage variable is defined it behaves exactly as before. Only if the
variable __usage is defined before main.sh is sourced the new logic
kicks in - in which case b3bp behaves likes a library (kind of).

[mstreuhofer]

if you are not totally against this PR i would go ahead and add tests for example.sh to cover this new sourced mode. also updating the documentation pointing out this new way of using b3bp would come your way.

[gdevenyi]

This looks great, would allow me to integrate my usage of b3bp.sh more tightly with upstream

[mstreuhofer]

that is the exact reason why i so furiously worked on all this changes ( #56 #57 and now #61 ). b3bp is really the boilerplate i need every time i start a new shell script. so much worked saved by just using it. but i am not a big fan of that copy-modify approach. what happens there is that you end up with 20 scripts which all started out as a copy of a different main.sh version, combined with different developers removing and changing as they will. deploying a new version of b3bp (e.g. super important bugfix) means changing 20 scripts instead of one "library".

[zbeekman]

LGTM

[mstreuhofer]

Oh and btw.. i would even go so far as to rename main.sh to b3bp.sh. If it is used as a template most people rename it anyway and as a "library" it deserves a proper name. Who's with me? ;-)

[kvz]

Thanks for your work @mstreuhofer!

i would even go so far as to rename main.sh to b3bp.sh

I need to think about that for a bit, I'm not immediately against it, I can say that.