Remove mapMany function

This duplicated F# core behavior from Seq.collect
Remove generic dependency on core run function

The generic runner was not really helpful in order to polymorphically
handle events, which should be needed in order to e.g. be able to select
different output formats at run time
Extracted code to new function

This allows us to test the bulk of the main function without actually
having to load assemblies with examples
Refactoring of reporter

Hopefully I will create a better commit message (or a better commit?)
Removed Success property from non-generic reporter
Changed ReporterWrapper to interface type

This could make it easier to create new reporters?
Changed changed exit code reporter into a class

This simplifies the code
Renamed ReporterWrapper to IReporter
Moved IReporter to TestReport.fs

It was temporarily placed in Runner.fs to allow refactoring of how the
runner would report to the reporter without affecting other code to begin
with.
Moved TreeReporter functions to higher scope

This allows us to use them from a new reporter type, natively implementing
IReporter
Refactored reporter test double
Removed unused functions
Moved ExitCodeReporter and wrapReporters to core

We will be needing them for the refactored runSingleAssembly
Removed old version of tree reporter