[datasets] Add a synthetic recognition dataset

[fg-mindee]

The library would greatly benefit from synthetic data. It could be very helpful for character classification, and text recognition.

Here are suggestions about the augmentations operating on discrete spectrum:

• choice of character in the vocab
• choice of font family
• choice of font style (bold, italic, etc)
  The last two would not be relevant for handwritten characters

And those operating on a continuous spectrum: all common image classifications augmentations (rotation, color modifications, etc.)

[felixdittrich92]

@fg-mindee
@charlesmindee
following #640 what is your idea to implement this or better what you expect to generate ?
My closed PR has implemented a Word-Image generator with the depending word labels where you can specify:

• language (vocab)
• image size
• background (noise /white)
• font (family / size)
• was planned also to add: rotation / distorsion / skew / blur

My orientation was a bit on this: TRDG
An example:

label: "sweat"

wdyt ? :)