When building the pending transaction we can call GetFee() to calculate
how much the transaction will cost. It takes a single parameter for the
number of inputs because we will want to specify how many when
estimating.
We then build a list of the potential fees for up to 300 inputs and pass
that to our output selection function which will use it to determine if
the outputs selected will be sufficient to cover the fees. This allows
us to know in advance how much the fees will be rather than trial and
error.
The Transaction Constructor will be used to generate pending
transactions, depending on the type of transaction the pending
transaction class will allow the user to modify items such as tx type
(ONS for example) add additional data to the tx extra field, modify burn
amount etc before finalising the transaction which will select the
necessary outputs, mixins and calculate fees and change amounts. Once
finalised the pending transaction will be forwarded to a signing
structure for further action.