Enable textual description/modification of hooks and orders

[colinschmidt]

Allow the user to supply a file that describes the order of steps/hooks they would like in something like yaml but looks like a simple text list of steps. In addition instead of the name of a step the user could put raw tcl in as a list element and hammer would then create an anonymous hook that includes that tcl at the point in the flow. This would lower the barrier of entry for new users adding hooks.

[harrisonliew]

Came up in discussion: this would be even more powerful if when sourcing/injecting the raw Tcl, hammer config variables can fill in for Tcl variables. This would further reduce the need for writing hooks in Python.