Test functionality with fake spell checkers
Switch to IPC::Run3 for simplicity and portability

Reading from both child's STDOUT and STDERR hangs on windows
(and is warned against in the IPC::Open3 docs).

I tried various other iterations (IO::Select, sysread, IPC::Run)
and this is the first one I got to work.
And it worked on the first try!
Merge pull request #2 from rwstauner/fake_checker

Use IPC::Run3 for portability and test with a fake spell check cmd