add fuzzy matching completion

[trbjo]

this commit adds a kind of fuzzy matching to zsh. example:

zshz <TAB> -> agkozak/zsh-z

with the previous behavior, zshz --complete could not resolve that.

If you do not want it to be the default behavior, I can add a flag to make it optional, for example ZSHZ_FUZZY.

[agkozak]

Thanks for proposing a contribution! I'm on vacation this week, but I'll take a look at your work in just a few days, OK?

[agkozak]

OK, I've put your code on the fuzzy branch so that I can play with it. I should have feedback in the next couple of days.