add support to log elapsedTime
Add 'D' pattern for elapsedTimeConverter
* Added support to the tomcat Server adaptor for correctly getting request start time. (Includes additional dependency on tomcat-coyote)
* Update layouts.html to document the addition of elapsedTime/D to the pattern support for IAccessEvent
* Modified AccessEvent.java to calculate the elapsedTime at construction of the event, instead of repeatedly in the getter.  This allows the value to be more easily seen in a debugger, and cleans up the code slightly.
* Fixed tabbing to be 2-spaces instead of 4
* changed direct access of timestamp field to use getTimstamp() instead inside of calculateElapsedTime.
* Undid some accidental roll-ups of imports, because my ide rules were set incorrectly.
* Added padding around NA, because my reformat took it away.
Merge pull request #152 from solidjb/master

Support for elapsed time to jetty and tomcat access logs