[#51595189] updated billing logic
Merge pull request #16 from dscataglini/51595189-legacy-bundle

[#51595189] updated billing logic
Updated rvm to use .ruby-version and .ruby-gemset
[#53035185] No longer using .rvmrc
remove 'Do Not Use in Production' warning from README because that ship has sailed
clean up README.rdoc
clean up whitespace in README.rdoc
add documentation
add Billing-Logic structure to README
define Independent/Single payment strategies
explain independent/single payment strategies' default payment_command_builder_class
remove outdated junk from README; add BaseStrategy info
improve README
improve README indentation
remove obsolete stuff from README
improve README
improve CurrentStateMixin documentation
improve README
add yard as dev dependency
improve BillingCycle documentation