Add an "ml upgrade" command that will automatically upgrade the Roxy files

[dmcassel]

I don't expect this command will cover all cases of going from any version to current, but it should be able to handle most of the work for most cases. Messages to the user about what to expect will be important.

Because a Roxy project has no explicit indication of which branch it's based on, the branch will be a required parameter.

Start off with a warning that this should only be attempted on a project that is in version control, so that rolling back will be easy. Only continue on confirmation.

Grab the following from the GitHub:

• deploy/* (recursively)
• ml
• ml.bat
• version.txt
• license.txt
• CHANGELOG.mdown

Replace the project's files with these. In addition, if the directory src/roxy/ exists in the local project, do a recursive update of those files, too.

[dmcassel]

Updated the Upgrading Roxy wiki.