chain/SkipIfStillRunning: fix bug handling different jobs It was an error in channel scoping that was identified in pull robfig#263. This adds a unit test to identify that issue and verify the fix.

docs: update and expand 

parser: fix combining of Dow and Dom Relevant portion of the spec (https://en.wikipedia.org/wiki/Cron): While normally the job is executed when the time/date specification fields all match the current time and date, there is one exception: if both "day of month" (field 3) and "day of week" (field 5) are restricted (not "*"), then one or both must match the current day.[3] When originally written, I incorrectly allowed restricted stars like "*/10" to trigger the "all must match" behavior. This bug would cause some schedules to run less frequently, or not at all. Fixes robfig#70

Update doc.go to fix description of @every 

Update doc.go to fix description of @every 

Fix usage example Fixes robfig#11