This adds support for SASS-style `@import` declarations, for transparently
including external `.scss` files in the resulting markup. File names are
resolved as per the rules set by SASS (i.e. importing a file named
"include/common" will search for "_common.scss" as well as "common.scss").
The entire source code had to be restructured around the idea of having to
switch the file context transparently, and is now based around double `while`
loops, one for checking the current context and the other for checking the
current line via `getline`.
The included test-suite may need some cleaning up, and the source code most
definitely will. More to come.
