func as option, option can be empty, defaults defined at entry point
more options, more flexible directory handling and prefixing
aligned with tests
cleaner iteration through assets
remove old options
added url for custom function
updated readme
version bump
Use four-space indents
Formatting changes
Remove console.error debugging line
Use url as the default CSS function for assets
Merge pull request #5 from conradz/options

Options, take 2