add orgtbl-ascii-plot package

I would like to submit orgtbl-ascii-plot package to Melpa.
- orgtbl-ascii-plot adds plotting capabilities to Org-mode tables, all in Emacs without external dependencies.
- full documentation here: http://orgmode.org/worg/org-contrib/orgtbl-ascii-plot.html
- GitHub home here: https://github.com/tbanel/orgtblasciiplot
- I am the author and maintainer.

This is my first contribution to Melpa (and any Elpa by the way).
I may miss something, so please tell me, I will fix it.

Regards,
Thierry Banel
tbanelwebmin@free.fr

| ! |  x | x^2 |              |
|---|----|-----|--------------|
| # |  0 |   0 |              |
| # |  1 |   1 | .            |
| # |  2 |   4 | :            |
| # |  3 |   9 | u            |
| # |  4 |  16 | W            |
| # |  5 |  25 | Wu           |
| # |  6 |  36 | WW:          |
| # |  7 |  49 | WWH          |
| # |  8 |  64 | WWWV         |
| # |  9 |  81 | WWWWH        |
| # | 10 | 100 | WWWWWW       |
| # | 11 | 121 | WWWWWWW-     |
| # | 12 | 144 | WWWWWWWWl    |
| # | 13 | 169 | WWWWWWWWWW.  |
| # | 14 | 196 | WWWWWWWWWWWV |
#+TBLFM: $3=$x*$x::$4='(orgtbl-ascii-draw $3 0 200)