ssl: allow setting cipher list
Merge pull request #83 from jmesmon/set-cipher-list

ssl: allow setting cipher list
Correct init mutexes and locking function

`libcrypto` uses locks quite intensively even without SSL. 
So they should be initialized before everything else to 
function properly in multi-threaded apps in which SSL 
operations are absent or delayed.

Finishes #79
Merge pull request #81 from vhbit/lock-init

Correct init mutexes and locking function
Better thread working

Works pretty stable for me, although I'm not sure it is 100% thread safe yet.

Changes mostly inspired by https://www.arangodb.org/2014/07/08/started-hate-openssl :

- Switched to newer CRYPTO_THREADID API for Unixes

- Clearing errors queue before every critical operation
Simplified SslStream.write, updated comments
Locking internal buffer from same thread access

If cloned stream was used in the same thread
WIP: erase later