Methods common to all steps object
==================================

A steps object represents a bundle of commands.  The base object has a list
of commands, but the most significant subtype of steps is trial, which does
not use this list any more, as the rules governing trials are more complex. 
*This list capability should be hived off to a subtype*

step
----

	some_steps step macro1=value1 macro2=value2...

Set the local macro variables `macro1` etc. to have the values `value` etc.,
and execute the command bundle.

report
------

	some_steps report

Emit the simple list of commands for `some_steps`.

clear
-----

	some_steps clear

Clear the simple list of commands for `some_steps`

add
---

	some_steps add any_command...

Append `any_command` to the simple list of commands for `some_steps`.

delete
------

	some_steps delete line_number

Remove the `line_number`th from the list of commands for `some_steps`

insert
------

	some_steps insert line_number any_command...

Insert `any_command` into the list of commands for `some_steps` before the 
`line_number`th command.