Reworked error output using abort(), aligned text in README, changed aur...

* Added function `ask()` for confirmation of overwriting existing package directory.
  * function re-asks for confirmation until proper input is given.
  * if answer is `no` error is given and `raur` is exited.
* Reworked error message output to use `abort()` for a more readable output.
* Reformatted `README.md` to align text better.
* Added `url` instead of calling the aur url directly.