find: Fix the `find` command, add more options. The `--endpoint` option doesn't make any sense anymore since page sources could have non-file-system endpoints. This was replaced with `--name` to match source names instead. Also added `--include-theme`, with filtering out theme pages by default, and `--exact` to explicitely match the given pattern, with matching anything that contains the pattern by default.

include README.rst
include CHANGELOG.rst
include LICENSE.rst
recursive-include piecrust *.py mime.types
recursive-include piecrust/resources *
recursive-include tests *.py
#global-exclude .DS_Store
#global-exclude Thumbs.db
#global-exclude Desktop.ini
#global-exclude *.swp
#global-exclude *~
#global-exclude *.bak