[BUGFIX] Run command is sent twice

The session is now run after the "session opened" event has been
processed.

Related: #2
[TASK] Refactor log listener

The listener now prints all sent commands and responses from the
debugger to stdout, using the prefixes [IDE] and [DBG], respectively.
Instead of relying on direct calls from the connection handler, it hooks
into the events as all other components do.
[FEATURE] Update session status from debugger responses
[TASK] Remove constructor from command interface

As we’ll need additional constructor parameters for some command
classes, the default constructor in the interface will get in the way.
[FEATURE] Store last known position in debug session
[WIP][FEATURE] Breakpoints in session
[BUGFIX] Debugger stream not properly closed
[FEATURE] Command for setting a breakpoint
[TASK] Add PHPUnit configuration
[DOC] Add dump of example debugging session

This dump was recorded with PhpStorm 7 and Xdebug; it can be used to
understand the basic mechanics of the protocol and its real-world usage.