Merge remote-tracking branch 'scraperwiki/master'
Style
Minor speed improvement by using tuples instead of lists
Fix spelling of error message
#61 All tablesets should raise the same exception.
Add CHANGELOG.
Merge branch 'master' of github.com:okfn/messytables
typo
Merge pull request #62 from scraperdragon/typo

typo
Merge pull request #63 from scraperwiki/unknownextension

Test for unknown extension, fix typo in error formatting
upstream merge
no duplicate horror
Merge pull request #60 from scraperdragon/htmltableset

HTMLTableSet
Add missing lxml dependency to setup.py
Improve readme.md
Update readme
Add contributing file
Move html tests to the end of test_read
Suggest to use PEP8 in contributing file
Extend contributing guidelines