Updated the change log for 5.4.0
Update graph string interp doc.
Updated User Guide on inter-cycle triggers at start-up.
Updated User Guide on warm starts.
Merge branch 'master' into release-prep-5.4
Documented triggering off tasks in other suites (by polling).

Also updated the User Guide for the recent REGDB changes.
Updated the change log for 5.4.0.
Change runahead tasks to held if beyond the stop time.

Closes #751.
Upped some test timeout intervals.
Fixed a doc typo.
Fixed another doc typo.
Merge branch 'master' into release-prep-5.4
Change log updated.
Merge pull request #731 from hjoliver/release-prep-5.4

Release prep 5.4
Merge pull request #768 from hjoliver/751.runahead-limit-and-stop-time

751.runahead limit and stop time