Bump min pdf-core version
:sparkles:
Nodoc Arcfour
Nodoc another security method
Resolve merge conflicts
Removed deprecation warnings on gradients

As well as deprecated ways to call these methods.
Merge pull request #674 from cheba/shading-deprecations

Removed deprecation warnings on gradients
Remove transactions and temporarily disable group

It does not seem likely that we will be able to stabilize
transactions in a general way any time in the near future.
I would like to restore a somewhat limited version of
the group() feature that does not rely on transactions,
but until we do, disabling the feature will make the
problem obvious right away to users rather than much
later via some hard-to-debug symptom.
Drop :optimize_objects feature because it is no longer used
Drop use of GC in soft mask
Use a version of PDF::Core without GC
Merge pull request #676 from prawnpdf/remove_transactions

Remove transactions and temporarily disable group
Add a failing test for broken margin behavior
Fix margin box setting
Mark test as resolved
Fix whitespace
Merge pull request #679 from prawnpdf/fix_margin_box

After exiting the top level bounding box, restore the current margins, not an old copy of them
Move grid into lib/prawn to kill off layout folder
Add missing 'free software' notices
We no longer need this folder