Implement character classes

[jehna]

VerbalExpressions should have support for all the available character classes.

Should we implement those as constants or just add them like in @andrii1812 's PR to Python repo:
VerbalExpressions/PythonVerbalExpressions#16

VerEx().find(VerEx.NUMBER)

vs.

VerEx().number()

[lukewestby]

lineBreak is already implemented as a method, and falls into a similar category even though it's not included in those definitions