Support for installing to specific path according to file extension and filename

This has been implemented to add flexibility to install paths depending on the type of file.
Currently, the install path is solely determined by the path extension. This pull request allows *extension descriptions* to determine the install path.
An extension description is the part of the filename before the final `.`, but coming after a preceeding `.`. For example:
`MyFile.font.css` - the extension is `css`, the extension description is `font.css`, and can be used to further sort large bower projects.

Tests have been written for this new feature. In amongst the PR there are whitespace fixes too, removing trailing tabs on certain lines.