Expand support for container id naming

[mikebrow]

Currently we limit container ids through regex to \w ascii numbers and letters and a few additional selected chars.

The spec has no such limit.

Suggest changing the code in one of the following ways to add the ability to support unicode names:

1. do a touch cid to see if the OS supports it as a filename and report otherwise
2. figure out how to the fix the expression for the plethora of unicode chars that should also be valid
3. hash the passed in cid, store the original in the container's state.. (slow)
4. @wrking suggestions: use percent-encoding or base64-encoding before using them as filenames

https://tools.ietf.org/html/rfc3986#section-2.1
http://tools.ietf.org/html/rfc4648#section-54

Opening the issue for discussion... I offer to do a PR based on discussions.

[mikebrow]

little interest shown