Adding iostream.h thread-safety documentation.#2995

Merged

rwgk merged 4 commits intopybind:masterfrom rwgk:iostream_h_thread_safety_documentation

Jul 12, 2021

+49-21

Commits on Jul 3, 2021

Adding iostream.h thread-safety documentation.
Ralf W. Grosse-Kunstleve
committed
Restoring TestThread code with added std::lock_guard<std::mutex>.
Ralf W. Grosse-Kunstleve
committed
Updating new comments to reflect new information.
Ralf W. Grosse-Kunstleve
committed
Fixing up git rebase -X theirs accidents.
Ralf W. Grosse-Kunstleve
committed