* Added -g option to shrink-path plugin.

The new optins adds an asterix to the uniquely shortened name, such
that, if copy'n'pasted, zsh globbing will expand to the full path name
of the shortened path:

shrink-path -g:
"/net/software/modules/modulefiles" -> "/n*/s*/modules/m*"

shrink-path -l -g:
"/net/software/modules/modulefiles" -> "/n*/s*/modules/modulefiles"

* Updated also the README file with the new -g option.

* shrink-path: improved handling of special cases

This commits improves the handling of special cases in path strings:

- handling of white space in path names
- handling of single-letter path names

* Update plugins/shrink-path/README.md
Co-Authored-By: Jacob Tomaw <jacob.tomaw@gmail.com>

* Fix typo "Asterix" and replace with "asterisk"

* Add optional quoting support to shrink_path
Co-authored-by: Jacob Tomaw <jacob.tomaw@gmail.com>