Refactoring commands; extract stats

Hi Peter,

This PR refactors sub-commands as standalone commands under 'cmd/cobe-*'.

- This decreases amassing of dependencies in the main command tool and
  allows to extract commands into their own projects should they grow
  too large easily.

- Starting to use cli pkg; adding usage and help information to flags.
  This harmonizes and increases display of usage information.

- Consequently using '-b, --brain' flag to allow specifying brain files.

- Dropping CPU profiling support from tool. Creating benchmark test
  with profiling enabled instead. Adding init subcommand for tool.

Also I've refactored the _statsd integration_ which now allows dropping dependency on statds pkg in core library: users are expected to use the cobe pkg as a library when there are more special cases to cover. Configuring a statter like statsd is still easy to accomplish using SetStatter.

However all stat'ing statements are left as is.

- David