Add an advanced text generator based on markov chains.

The advanced text generator's text()-generator is compatible to
Lorem's one and can be used as a drop in replacement.

see fzaninotto/Faker#109

Examples (The number is the maximum amount of characters, the line breaks are here for better formatting and not generated):
```
  10: Poor.
      
  20: The Duchess tucked her.
      
  50: Mary Ann, what are you getting on?" said the Hatter, and he.
      
  70: This time there could be no mistake about it—it was neither more nor l
      ess than a.
      
  90: She drew herself up and said very gravely, "I think I must be off, and s
      he dropped it hastily, just in time to.
      
 120: Very soon the Rabbit came up to her great delight, it fitted! Alice open
      ed the door and tried to make out which were the cook took the least not
      ice.
      
 150: I should like to be talking in its sleep, "that 'I breathe when I breath
      e!'" "It is the same height as herself. She stretched herself up on tipt
      oe and peeped over the list. Imagine.
      
 200: She stretched herself up on tiptoe and peeped over the list. Imagine her
       surprise when he finds out who I was when I get it home?" when it saw h
      er. "Cheshire-Puss," began Alice, rather timidly, "would you please tell
       me your history, you.
      
 500: However, when they liked and left off quarreling with the others. IX—W
      HO STOLE THE TARTS? The King and Queen of Hearts, she made some tarts, A
      ll on a summer day; The Knave of Hearts, carrying the King's crown on a 
      bough of a book," thought Alice, "without pictures or conversations in i
      t, "and what is the same thing," said the Cat, and vanished. Alice had f
      ound her head pressing against the ceiling, and had no reason to be seen
      —everything seemed to quiver all over with William the Conqueror." So 
      she was now the right paw 'round, "lives a March Hare. Alice gave a wear
      y sigh. "I think you ought to.
```