Enhancement Release: unicode and security

1. We now have full Unicode support. See Issue 167 for details, including the new --config-file-encoding command-line option.
2. We now support secure handling for all credential settings and credential files. See Issue 159 for design discussion, and read the docs for associated config changes.

NOTE: This release is stable and can be used reliably by customers who need the additional security or unicode features. We have left the pre-release flag on because customers have discovered issues on Linux and Windows with security (#199, #198). We will issue a double-dot that fixes these issues.