Add `fleece build --include` option to explicitly include files/directories in builds

[larsbutler]

This came up in the discussion on #75. Instead of pulling entire directories (using --source) and excluding unneeded files (using --exclude), in some cases it would be useful to simply explicitly --include only the files that are need in the built Lambda function zip file.

Here's what I'm thinking:

• --include should work for single files or to recursively include entire directories
• One or more --include parameters can be combined with one or more --exclude parameters to precisely select the set of files to include in the built zip
• Support for glob patterns