Add new generic TLS error code
tls short read in state closed is no longer an error
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add socket/security policies to translate asio -> websocketpp error codes

The reason these were added to the socket policies rather than higher
up is that in some cases translating error codes requires information
from headers and libraries that are not present except when certain
socket policies are being used. For example, SSL/TLS related errors can
only be translated using openssl, which is only pulled in with the TLS
socket policy.
cleans up the handling of TLS related transport errors

Specifically: TLS short read is separated from other TLS errors. Other
TLS errors are also not separated from generic “pass through” errors.

TLS short read is now considered “expected” during socket shutdown and
is not reported as an error.
update changelog
Merge pull request #331 from zaphoyd/tls_short_read

Tls short read related changes references #263
work on close step
Use clang on OS X by default for building examples and tests
Add method to look up a human readable string given a close code value
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Merge branch 'master' into tutorials
Finish app client tutorial step 5 (closing)