Use newer fixed-width numeric typedefs in header files

We want to show a unified API system in our header files. We still have
a long way to go with other stuff, but the lcb_Uxx has proliferated most
of the codebase already so it's time to just change everything over.

Change-Id: I3890bc050b3b5a77356fcbc9e56e1c04464ef7e2
Reviewed-on: http://review.couchbase.org/39059
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Expose retry interval and backoff settings

- LCB_CNTL_RETRY_INTERVAL (how often to retry)
- LCB_CNTL_RETRY_BACKOFF (factor by which interval increases for each
  additional retry)

Change-Id: I12a8a791f2897d17acf85ebec5da91c4f38730c7
Reviewed-on: http://review.couchbase.org/39141
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>
CCBC-226: Use keepalive for views

This changeset creates a socket pool (lcbio_MGR) instance for HTTP
connections. In order to avoid situations where a pooled connection is
no longer functional, its use scope is limited to view requests and the
socket is only placed back into the pool if the underlying parser object
(via http_parser) indicates that the connection is keepalive-enabled.

Change-Id: I063ffcc67feee990d489816dbbd184e9affe7ad3
Reviewed-on: http://review.couchbase.org/39146
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>