Non buildable. Interface and stubs for classes: Subscriber, Call, Refill
Rename attributes in class Call.

Delete constructor without arguments in classes Call and Refill.
Fix interface of class Subscriber.
Fix class BillingRules. Add forwarding.
Fix stubs and method charge in class Subscribes.
Use ifndef instead pragma
Implementation class Call
Implementation class Refill
Implementation class Subscriber
add getters in Subscribers.

Replace tabs.
Fixed some methods, cyclic relation
Insert spaces.
Added more DefaultBillingRules tests.
Fix Refill's constructor.
Using <regex> and fix constructors.
Change formating.
Formatting
More formatting.
Formatting.
Add default constructor to BalanceIsEmpty.

std::logic_error has no constructor without parameters, it must be
initialized with an error message.