renames to make Simpler less wordy

`T`, `I,`, `O`, and `IO` replace `Task`, `InTask`, `OutTask`, and `InOutTask`. The wordy names for these classes are preserved in `Simpler.Wordy`.

These four classes are used over and over again so switching to the one or two letter class names reduces clutter in files. 

This also sidesteps namespace issues with `System.Threading.Tasks.Task`.