Don't throw undefined method when form_group content block returns nil

Fixes #111
Merge pull request #112 from bootstrap-ruby/fix-nil-content-block

Don't throw undefined method when form_group content block returns nil
Update CHANGELOG.md

Add #111 fix
prevent exception on human_attribute_name when using bootstrap_form_tag. fixes #115
Added support for additional class to the wrapper form_group by a field with the option `wrapper_class: 'additional-class'`
Accept an array of checked values for #collection_check_boxes

Fixes #110
Merge pull request #114 from bootstrap-ruby/multiple-checked-values

Accept an array of checked values for #collection_check_boxes
Updating Changelog
fix using check_box with bootstrap_form_tag
Merge pull request #117 from datWav/master

Added support for additional class to the wrapper form_group by a field ...
cleaning up the README regarding form group wrapper classes
Fixing some misplaced changes
Cleaning up the README.

Attempted to group related items together and make it clear that this gem provides a wrapper around the standard Rails form helpers. Closes #105.
Simplified alert_message error summary logic. Error summaries are now enabled by default, but can be disabled by setting alert_message's :error_summary option to false.
Merge pull request #119 from rosswilson/master

Support showing error summaries when inline_errors is enabled
updating CHANGLOG and README for #119
fixing typo in README
README tweak
Merge branch 'check_box_fix' of git://github.com/burnt43/rails-bootstrap-forms into burnt43-check_box_fix

Conflicts:
	lib/bootstrap_form/form_builder.rb
Merge branch 'burnt43-check_box_fix'