Conditional async_client liftetime_thread creation

Create a thread and add it to io_service only if io_service is internal. If internal - do not change it.
HTTPS Client Feature Documentation

These are the source-level changes to document the HTTPS support in the
client. This is useful in explicitly spelling out how to build the
client libraries to support HTTPS URIs in the client.
Add generated HTML
Fix uri swap crash
Fix tabs
Update HTTP Server documentation.

Fixes #387
Merge pull request #433 from deanberris/0.11-devel-docfix-server

Update HTTP Server documentation.
Create thread in async_client when io_service is own

Fixes a bug in previews commit when if was inverted.
Merge pull request #431 from eakraly/0.11-devel

Conditional async_client liftetime_thread creation and fix for URI swap bug.