feat: implement basic character classes

[mdjastrzebski]

Scope

Implement base character class components:

• digit
• word
• whitespace
• any

Suggested API

let regex = buildRegex(
    digit(),
    word(),
    whitespace(),
   any(),
)

Refs

• https://developer.apple.com/documentation/regexbuilder/characterclass/word
• https://developer.apple.com/documentation/regexbuilder/characterclass/digit
• https://developer.apple.com/documentation/regexbuilder/characterclass/whitespace
• https://developer.apple.com/documentation/regexbuilder/characterclass/any

Related Issues

[jaworek]

I'll take whitespace character class and possibly other when it is done.

[mdjastrzebski]

@jaworek go ahead. Whitespace probably need to just emit \s. Actual work is needed to modify the DSL to support it.

[okwasniewski]

Implemented in #13 by @jaworek