Provide a shorter namespace

[bahmanm]

Offer the user to use either bmakelib or other shorter namespace(s).

For example:

some-target : bmk.error-if-blank( VAR1 )

or (🝼 represents "Makemake" the god of fertility in Polynesian mythology)

some-target : 🝼.error-if-blank( VAR1 )

or even

some-target : 🕮.error-if-blank( VAR1 )
some-target : 🏗.error-if-blank( VAR1 )
some-target : 📚.error-if-blank( VAR1 )

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See also #80