Enable possibility to user control $CGIBASHOPTS_DIR

[Aufschlauer]

The default directory /tmp for $CGIBASHOPTS_DIR is often on a different partition than the root filesystem. So moving a file from /tmp to the root filesystem might take some time. This PR enables the possibility to control where $CGIBASHOPTS_DIR points to.

[ColasNahaboo]

(sorry for the delay).
Nice useful suggestion.
However, I will rather have the user be able to change "/tmp" by something else rather than the whole CGIBASHOPTS_DIR, to avoid the risk of the user forgetting to add the unique part "$$". Is that OK with you?

Something like:

CGIBASHOPTS_TMP=/www/tmp
. cgibashopts

Will thus make cgibashopts use internally CGIBASHOPTS_DIR=/www/tmp/cgibashopts-files.$$

Would that be OK with you?

[ColasNahaboo]

Implemented - differently - by the new option -d in Release v4.1.0 https://github.com/ColasNahaboo/cgibashopts/releases/tag/v4.1.0