Support for "MIXED" string case

[YroslavNykolyshyn]

I haven't found a good way to handle string data generation for custom MIXED case.
I noticed that you recently added the ability to select the string type.

New setting Keys.STRING_TYPE
The new setting allows customising generated string types via Settings:

Comment comment = Instancio.of(Comment.class)
    .withSetting(Keys.STRING_TYPE, StringType.ALPHANUMERIC)
    .create();

or globally using instancio.properties:

string.type=ALPHANUMERIC

Could you also add an option to customize the string case?
New setting Keys.STRING_CASE

Comment comment = Instancio.of(Comment.class)
    .withSetting(Keys.STRING_CASE, StringCase.MIXED)
    .create();

or globally using instancio.properties:

string.case=MIXED

[armandino]

@YroslavNykolyshyn thanks for the suggestion. Will be added in the next release.

• Add a new setting for String case #1051