Modify lexer to use Arc.

This allows sharing of the input string between tasks without copying.
Move `almost_equals` to `json_almost_equals`

It is useful for general JSON comparisons.
Move `specfold` lexing to "spec_css/lib.rs"
Make `specfold` wait for results with single task

Since there is no need to do validation when there is only a single
task, `specfold` was completing immediately when given only one task.
spec_css: Correct parsing all tests.
spec_css: Remove debug code.
Remove excess whitespace
Only send to the coordinator when worker is done.

Rather than sending each extracted `Node` over the `Chan`, send a vector
of `Node` structs when the worker is done. This drastically reduces the
overhead of sending over channels.
Switch to testing the parallel speculative lexer.