ScheduledBasicBlock::get_waveform_duration_seconds previously assumed that the duration of all built-in waveforms is equal to their duration parameter. This isn't true for erfsquare, though; the duration parameter just specifies the duration of the active pulse, and the padleft and padright parameters specify silent padding on either side which contribute to the total duration.

This PR updates the computation of the duration to include the padding. This is a breaking change, because now scheduling a program with an erfsquare waveform requires that the erfsquare waveform have these extra parameters and that they be constants. Indeed, some of our very own tests were broken by this.

There is also some inconsistency in names, which this PR papers over by accepting both:

• The Quil spec calls the waveform erfsquare, but our test cases call it erf_square
• The Quil spec calls the padding parameters padleft and padright, but our ErfSquare type calls them pad_left and pad_right.

As implemented, any mix of the underscoreless and underscoreful names can be used.

Closes #405.