Added beginning_of_minute support to core_ext calculations for Time and DateTime
Merge pull request #9365 from gaganawhad/core-ext-beginning-of-minute

Added beginning_of_minute support to core_ext calculations for Time and DateTime
fix time_tag helper and update tests to not rely on dynamically generated values

  Before `time_tag Date.today` will return `<time
  datetime="2013-02-14T00:00:00+00:00">February 14, 2013</time>`.
  This commit fixes time_tag helper to use RFC-3339 full-date format
  (Y-m-d) in datetime attribute.
document setting custom datetime attribute for time_tag helper
Merge pull request #9334 from NARKOZ/time_tag

use ISO 8601 format in time_tag helper