Grammar.parse :args support

See https://github.com/perl6/specs/commit/67579a1cf7
https://github.com/perl6/roast/commit/1bc8a5fee6
Pass on --ll-exception in precomping process
Lazily initialize $*THREAD
update ROADMAP

* add @<> regex feature, vendethiel++
* remove duplicate mention of coercions
Mention Proc::Async

Even though it was in the previous release already
Add Kernel.signal to get kernel signal values

Either takes a string, or Signal Enum.  Please note that we cannot reliably
map the Signal Enum to Kernel signal values, as these may (and do) differ per
kernel.
Get Kernel.signal up to spec  :-)
Again, bring Kernel.signal up to spec
Add Str.IO.watch, remove need for code stubs

This will probably need a reconfigure to work.
Fix copynpasto/thinko in chars/bytes logic
Streamline Supply generating code
Implement :%ENV for Proc::Async.start, as per spec
Make Proc::Async not work in restricted setting
Better default handling for Proc::Async's :ENV
say is a print, why not in the async case as well?
Merge pull request #279 from cognominal/patch-1

Grammar.parse :args support
initial fix for hanging Str.lines on parrot
Temp fix for other candidates, RT #122783
Mention #122783 for posterity
Add basic Proc::Async test for moar only