Move getEnvIO over to the base module, and rename it getEnvMaybe
Add a getProcessorCount function
Fix up --lint-tracker with high levels of parallelism
Fix up getProcessorCount on Windows
Change all the int arguments to take an explicit lower bound, and give clearer error messages
#82. make -j0 guess at the number of processors
Add a random sleep, otherwise sometimes the basic test fails on my laptop
Add a test for -j0 and -j2 both producing some level of parallelism
Improve the docs dependencies, should depend on all of General as well, but not Ninja/Make pieces
Don't run the docs test with --lint-tracker, it includes things I don't care about
Generalise allowCreate to trackAllow
Update the docs to be fully --lint-tracker correct