CCBC-540: Document durability interval as microseconds
CCBC-540: Document durability interval as microseconds

Change-Id: Ib01d8efe273b2f8753598c7b5e7a9a7cfc86764a
Reviewed-on: http://review.couchbase.org/42907
Tested-by: Mark Nunberg <e7d42768707bf23038325b0b68d4b577e5f6064a@haskalah.org>
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>

maxim-ky/libcouchbase,couchbase/libcouchbase,senthilkumaranb/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,mnunberg/libcouchbase,maxim-ky/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,kojiromike/libcouchbase,signmotion/libcouchbase,PureSwift/libcouchbase,avsej/libcouchbase,mody/libcouchbase,kojiromike/libcouchbase,senthilkumaranb/libcouchbase,signmotion/libcouchbase,maxim-ky/libcouchbase,signmotion/libcouchbase,maxim-ky/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,mody/libcouchbase,mnunberg/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,mnunberg/libcouchbase,kojiromike/libcouchbase,mnunberg/libcouchbase,senthilkumaranb/libcouchbase,avsej/libcouchbase,mnunberg/libcouchbase,avsej/libcouchbase,PureSwift/libcouchbase,mody/libcouchbase,signmotion/libcouchbase,PureSwift/libcouchbase,mody/libcouchbase,avsej/libcouchbase,avsej/libcouchbase,PureSwift/libcouchbase,senthilkumaranb/libcouchbase