Add option to abbreviate home directory to ~ when searching

[d3dave]

WHAT

Adds a new boolean option (ENHANCD_FILTER_ABBREV) that controls abbreviation of the home directory prefix (determined by $HOME) to ~ when searching interactively. Implemented for both zsh and fish.

WHY

I most often search through paths under my home directory. As a result, I see a bunch of entries that all begin with /home/my_username:

/home/my_username/code/python/cpython/PC
/home/my_username/code/python/cpython/Parser
/home/my_username/code/python/cpython/Objects
/home/my_username/code/python/cpython/PCbuild
...

Enabling ENHANCD_FILTER_ABBREV reduces these to look a lot more concise and less cluttered, like this:

~/code/python/cpython/PC
~/code/python/cpython/Parser
~/code/python/cpython/Objects
~/code/python/cpython/PCbuild
...

[babarot]

Thank you for adding new feature