Support 3 letters for weekday names

[Raol87]

Is your feature request related to a problem? Please describe.
In some languages, two characters is not enough to distinguish between weekday names. A lot of other date pickers, such as jquery date picker, support three characters to resolve this.

Describe the solution you'd like
Allow for weekday names to use three characters.

Describe alternatives you've considered
There really isn't another solution.

Additional context
N/A