Support job payloads as JSON or text/plain

"Clever Gearman Koans, in the style of http://stevelosh.com/blog/2013/04/git-koans/"

```
A novice programmer and a gearman master were walking along the pathway, discussing gearman architecture. 

"Master" said the novice, "I have built a gearman worker".

"Indeed" said the Master. "There is only one more thing you must do. The worker should accept jobs with plain text payloads"

"But master" inquired the student, "in the past jobs have used json payloads. Why suddenly has that changed?".

"It is the gearman way" said the master.

The novice ran off, eyes furrowed in enlightenment. 

"Master" the novice said, returning. "My worker now accepts jobs with plain text payloads, for it is the gearman way".

The master nodded in approval.

"Pray tell" said the student, "how do I submit jobs to my worker through the job server?".

"It is impossible" said the master.

The novice nodded, enlightened, for it was the gearman way. 
```