Sync with upstream version 5.3.3

Update to Proguard 5.3.2

Remove changes which are now obsolete

Improve synchronisation so we don't enter the sync block unless we need it

Update to Proguard 5.3.1

Applied patch to take base from 5.2.1 to 5.3

Merge pull request #10 from drewhannay/patch-1

Fix build.xml path in README.md build command

Store intern version of strings to avoid duplicate strings being created on the heap

This change can cause some problems with classes, and so is being reverted.

Don't force a switch back when a byte array is needed and ensure that any Strings are the intern version

intern the type value to avoid duplicate strings taking up memory

remove patching artifact

Merge pull request #9 from imperio59/strings

Remove class which came over as part of the rebase