Added composite logging

Allows use of multiple logging factories (e.g. console and file)
Merge branch 'composite_log' of github.com:roji/quickfixn into composite_log_180
credit for #180
add IDisposable support to CompositeLog (#180)
Merge pull request #192 from connamara/composite_log_180

CompositeLogFactory - original #180 plus IDisposable support