[boost] [Date_time] Adding Input Format Flag Parsers

Subject: [boost] [Date_time] Adding Input Format Flag Parsers
From: Yucheng Low (ylow_at_[hidden])
Date: 2015-10-08 18:24:17

Hi,

Boost date_time is missing a bunch of format flag parsers on input 
(%I,%l, %P, %p).

Here is a proposed patch to add these format flags.

Thanks,
Yucheng