[Fix #605] Ensure that resource file urls are decoded and correct on Windows.

cider--resource-file-url-to-file function created that extracts
the filename from the url, decodes it, and drops the leading '/' if
the path is a Windows path.
Use cider--resource-file-url-to-filename to get jar path.
Merge pull request #658 from scottdw/fix-605

[Fix #605] Url decode resource URLs and remove leading '/' from windows paths.