Add support for Last Day of Month ('L')

[sauravhaloi]

Add a special character 'L' in the day-of-month field, which specifies the last day of the month

e.g: '0 0 18 L * ?' denotes the following:

At 6:00:00PM, on the last day of the month, every month

[wjm3219]

是不是考虑下支持 '0 0 1 15,L * *' 这样的呢? :)

[wsq2025]

why now master branch not support L for last day of month

[xuyang2]

是不是考虑下支持 '0 0 1 15,L * *' 这样的呢? :)

http://www.quartz-scheduler.org/documentation/quartz-2.3.0/tutorials/crontrigger.html

When using the ‘L’ option, it is important not to specify lists, or ranges of values, as you’ll get confusing/unexpected results.