Only examples defined in the "examples" field are generated, if they are
defined in "example", they are just ignored.
Also fix a bunch of incorrect tests.
When the string transformation to number failed, all following
transformation failed too.
This happend because status in decNumberFromString function is
updated just in error case. Reusing the DEC_CONTEXT that failed
before results into error even if the string is valid number.
Keep a cached copy of the man tests that we can use when no manpage
changes are made. This allows automated systems that might not have
easy access to a pipenv to build and run tests.