Added functions for new shell banner.

This change does the following:
 * provides a new banner for the LFE shell, inspired by the Julia shell
 * splits out functions for creating the banner, thus:
 * laying the foundation for support for shell overrides (e.g., updating the abort command message for different backends, like Erjang)

The shell banner proposed in this change is as follows:

```
Erlang/OTP 17 [erts-6.2] [source] [64-bit] [smp:8:8] [async-threads:10] ...

      (
   (   )
    )_(_(
 .-(  \\ )-.       | A Lisp-2+ on the Erlang VM
(    / \\   )      | Docs: http://docs.lfe.io/
|`-..___..-';--.   |
|       g  (__  \  | Type `(help)` for usage info.
|      n    | )  ) |
|     a     |/  /  | Source code:
|    l      /  /   | http://github.com/rvirding/lfe
|   r      (  /    |
\  E        y'     | LFE v0.10.0-dev
 `-..___..-'       | LFE Shell V6.2 (abort with G^)

>
```