feat(tmux): sessions named as current dir

[jfpedroza]

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.

Changes:

When $ZSH_TMUX_AUTONAME_SESSION=true, name the tmux session after the working directory.

If you are in ~/foo/bar, the name will be bar. If you are in ~/, the name will be home.

[carlosala]

I like it! I'm ok with merging it! I'd name HOME in caps; it's less common to have a directory called HOME than home.
The only thing that's missing is a special case for /. Maybe ROOT?

[jfpedroza]

Never considered opening a session at /. I agree with ROOT.

[carlosala]

Thanks for your contribution!