Fix an issue in tclspec when errors happen during the loading of spec files.

This fixes a bug that caused tclspec to exit succesfully, when it should've
actually just errored out.
Convert Spec::World from NX to TclOO.
Convert Spec from NX to TclOO.
Add an almost complete Mock backend for TclOO.
Convert Spec::Example class to TclOO.
Port Spec::Hooks and Spec::Configuration to TclOO.
Fix some more issues caused by moving to TclOO.
Swith the Runner implementation to TclOO.
Port the Reporter to TclOO.
Also port formatters to TclOO.
Port expectation handlers to TclOO.
Ported ::Spec::Matchers to TclOO.
Fix an issues where failure messages would not contain any example description.
Port all matchers to TclOO.
Remove the namespace nesting example and replace it with namespace import.

Namespace nested describe blocks was not really reflecting how namespace
nesting works in TCL itself.
Port Spec::ExampleGroups to TclOO.

This has some backwards-compatibility breaking changes, because NX gave us
fully private namespaces (due to a different variable resolver
implementation).

Variables inside before all/each blocks now have to be declared with
"variable", if they should be available inside examples.
Disable output buffering in formatters.