Add local-config plugin.

Support per-user, per-host, and per-platform custom configuration files.

Stops theme breaking in root directory

new plugin:better alias

Rewrite `bundle exec` wrapper to be more robust

Improve syntax and uniform style for plugins’ README

Add support for ST and ST3 installations inside `~/Applications` on OS X

Add eclm theme

add virtualenv section to agnoster-mercurial prompt

Allow to pass any arguments to z

before:

```
$ z --help
12         /Users/Jean/Dropbox
12         /Users/Jean/work

$ z work
/Users/Jean/work
```

after:

```
z --help
z [-chlrtx] args

$ z work
/Users/Jean/work
```

- prompt line enumeration implemented
- new function to set the window title
- new session history
- README file updated
- replaced all `math` commands by `expr` for better performance

- Bookmarks and command/directory history functions implemented
- Function to edit commandline with $EDITOR
- Faster git parser