HV-809 Some style, formatting and comment improvements
Cleaning code for HV-809

Based on the chages done by @gunnarmorling and feedback from #270

- ModCheckBase: removed multiplier attribute

- Mod11Check: change multiplier to threshold, threshold now defaults to
Integer.MAX_VALUE

- Mod10Check: added multiplier option since is no longer present in
ModCheckBase.

- Update CPF, CNPJ and TituloEleitoral constraints

- ModUtil: Changed the variable names for better understanding
HV-809 Avoid repeated stripping of non-digit characters
HV-809 Making some members private; Compiling regex pattern for re-use
HV-809 Updating reference documentation