Option to override step path

[GideonBear]

Example:

[hx]
path = "not_hx"
# Or:
path = "/usr/bin/hx"

We simply have a default value of hx and let the user override it. which should be able to handle absolute paths just fine.

This could help when a user has conflicting binaries installed, and

1. has renamed one of the binaries
2. uses the full path / has aliased the full path

(thx @uwuclxdy)