Issue 192: support for duration

Revised text:

1.  In clause 10.3.1.3, in the list following "FEEL supports the following datatypes:", REPLACE the bullets:
•	duration
	o days and time duration
	o years and months duration

WITH:
•	days and time duration
•	years and months duration

2.  In clause 10.3.4.1, in Table 54 (Beta-3), in the row for ‘years and months duration’, in the Description column, REPLACE:
“return duration between from and to”

WITH:
“return years and months duration between from and to”