Allow numbers to be displayed.

[eriknyk]

When we have a text by example: 123456
it should be displayed: (12) instead of the current placeholder icon
I think placeholder should be displayed only when there are not valid characters like #@#$%^&...
however numbers still are valid, another example is: 1Alpha it should be displayed (1A) as icon text

[Fi5t]

@eriknyk thanks for your interest in this library. I'll review this issue a bit later.