added SSLSocketAppenderBase and supporting classes to core

In addition to the new base appender, this commit includes several
supporting classes that are used to create and configure an
SSLContext and all of its constituent components, and corresponding
unit tests and resources.
added SSLSocketAppender to classic

This commit adds the new appender and modifies the
DefaultNestedComponent rules to include rules for SSL configuration
types.
added SimpleSSLSocketServer to classic

This commit adds the new server and modifies SimpleSocketServer so
that its startup logic can also be applied to a SimpleSSLSocketServer.
added SSLSocketAppender to access

This commit adds the new appender and modifies the JoranConfigurator
to include rules for SSL configuration types.
added documentation for SSLSocketAppender to manual

This commit modifies appenders.html to include information about
SSLSocketAppender, and adds a usingSSL.html (linked from the
relevant sections of appenders.html) that describes the SSL-related
configuration properties.
Merge pull request #84 from ceharris/LOGBACK-818

LOGBACK-818: support for SSL-enabled socket appender and server