Merge pull request #673 from getnikola/pigz

Support for pigz or other external gzip commands (Fix #351)
Fix #680
Merge branch 'master' of github.com:getnikola/nikola
updated pt_br translation
6.0.2 because f*ck it
Addresses several issues in #704

- Avoids shell=True and hence any quoting issues
- Cleans up temporary directory

This code has not been run since FILTERS don't appear to be tested.
Don't bother creating temp directory unless it is needed
Typo (Fix #706)
Merge pull request #707 from rogerbinns/issue-705

Addresses several issues in #705
updated changelog
flake8 fixes
Fix #708
fixed conflict