make texas.zsh executable

[teranex]

This commits makes texas.zsh executable and adds a shebang so that texas.zsh can be executed directly.
My reason for doing this: In Rofi I use a custom script to list my most commonly used directories and quickly open them in the file manager. I now switched this to launch Texas, but simply running terminator -e texas doesn't work (I guess because $fpath is not defined in that case?). Running terminator -e /path/to/texas.zsh works without any problems. I don't think this has any side-effects.

[vifon]

Did you try to setup your $fpath and autoload texas in ~/.zshenv instead of ~/.zshrc? It might help. I'm hesitant to make texas.zsh executable because of its tricky launch procedure.