build: replace verstion extraction via set to use python The version of roundup was extracted from roundup/__init__.py by sed. It is used to label the roundup.pot template file. Replaced the sed setup by importing roundup and printing the __Version__ variable. This should be less fragile to spacing and other changes.

try:
    # Python 3+
    from ssl import SSLError
except (ImportError, AttributeError):
    # Python 2.5-2.7
    from socket import sslerror as SSLError  # noqa: F401