remove Gemfile.lock
Merge pull request #499 from nanoc/bugfix/remove_Gemfile_lock

Remove Gemfile.lock
Fix many Rubocop offenses

This is the second part of my crusade against non-standard code style;
the first part being #476. There are two reasons why these changes were
not in #476:

1. Rubocop got updated with a lot of new checks, and this PR ensures we
   adhere to the guidelines set forth in that new Rubocop.

2. I got over the attachment to my personal preferences (such as TODO’s
   not being postfixed by a colon).
Merge pull request #500 from nanoc/more-style-fixes

More style fixes
Fail tests on Rubocop failure
Merge pull request #501 from nanoc/fail-tests-on-rubocop-offenses

Fail tests on Rubocop failure
add support for :extra_files config whitelist for extra files, update #492
Test support for dotfiles in data-sources

    .htaccess and .htpasswd were not handled by any data-source
fix code and tests
improved documentation and errors for all_files_and_dirs_in
add more tests for all_files_in