Bumped up the version number

Retroactively added Python-requires to setup.py

Don't spin up new threads if there are existing idle ones

Fixes #88.

Bumped up the version number

Bumped up the version number

Fixed OverflowError with ProcessPoolExecutor on Windows

Made thread joins interruptible by specifying a timeout (fixes #25)

Updated the changelog and bumped up version

Bumped up version

Bumped up version