Reformat Item initializer lists

Make it easier to see how they are similar/differ.

Change-Id: Ia140dc18d5445d93aca4ac943ce481a5dcf2fd8d
Reviewed-on: http://review.couchbase.org/42623
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>
Move Item member initialization to initializer list

More refactoring to prepare for merging consturctors, also is more
efficient as we don't default construct the std::string for key before
assigning it.

Change-Id: I3c6e45ea9f3303e5d29f7231ae282f1d59efb31c
Reviewed-on: http://review.couchbase.org/42624
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>
Remove unnecessary Item() constuctor #2

Remove another constructor of Item, the one which takes only a data
size - i.e. allocates a value but doesn't copy it in. In all existing
use-cases this can be replaced with either:

a) The constructor which does copy the data in, as the use-case was
   doing performing the copy in two stages (construct Item of correct
   size, then memcpy()).

b) The consturctor which takes both ptr and size, with with ptr==NULL
   - this is already handled by the setData() private method of Item.

Change-Id: Iffbfef423e82bb021f74860a72dc7b5936bf2215
Reviewed-on: http://review.couchbase.org/42625
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>