dynamic history

Previously, all specs had to be pre-allocated by using the 'add_history'
function. This is now no longer required and instead serves as a hint to
the HistoryContainer to pre-allocate the space for the given spec.

History can grow by increasing the length for a frequency, adding a
frequency, or adding a field. It can grow with any combination of
these.
To simplify this, I am just removing the notion of changing `cap_multiple`, I am also removing the check here. The assumption will be that the caller has verified that a resize needs to happen.