Dismantle test_manual.py.  (Failing tests not yet readded.)
Remove lingering references to rule.index.
Clean up handling of !default.
Fix UnparsedBlock properties when the header rewrites its prop.
Remove a few unused vars and args from the guts of the output code.
Boolean attribute for string source files
Cleanups, variables names fixed, small issues fixed
Added background-brushed
Interpolated mixins names normalized
Logging handler for tests added
Do not return undefined elements when calling first()
Reverting bits of adc10d7e3a244020eb462d1464326182c637c30d (causing TypeError: can't multiply sequence by non-int of type 'float')
Added some tests
Loop variables are normalized