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

now it works with sublime 3 on arch linux

rvm plugin fix #217

Budspencer theme

from bpinto. Thank you very much.

removed needless colors
comments inserted