Remove todo from readme, since its in GH issues
Fix data races in test suite

This fixes the data races in the test suite, when ran with `go test
-race`.

The new behaviour is the same and fzz works the same. The fix also
removed the wrong behaviour of `return`ing to early and not resetting
the printer when a command failes with an error.
Fix data race by not removing shared access to input slice
Bring back the Printer mutex

This reverts commit dbba735421401c4751a1cf8c5eb29ef666ca6679.
Avoid reading incomplete utf8 sequences