This is a partial backport of commit 8e3a0eb1 at p2
icc: fix for intel compiler icc
jit x86_64 branch-prediction optimization

use 2-byte repz ret instead of single-byte ret to help branch-prediction.
See http://repzret.org/p/repzret/
Revert "jit x86_64 branch-prediction optimization"

This reverts commit accb2b59a80ee5893816c0cd680a5a121994de28.
backport -Dt and -Dc from p2

-Dt enables -B per default. -Dc only rudimentary yet
potion #9: fix parser is not re-entrant, but still not GC safe

All the intermediate t and lhs objects in the compiler need to
be moved also while in a eval, and be checked for FWDs.
README update

floating point support is now ok
coros are limited (no ppc, rather check out ucontext)
mention eval problems and os threading plans
README: add nice GC number
backport README indentation fixes from p2
move away test/flow/eval.pn to test/misc/eval.pn.notyet

issue #9 GC-safe re-entrant parser
fix test/numbers/to.pn syntax
signature default param:=value

does not compile yet
greg: add yyqq(), quote strings dumped to source code
add -DP PARSE_VERBOSE, fix yyqq (null term), add -D?

-DP prints now the verbose parse steps, so you can do -Dpv
without verbose parse output.
merge greg with 4.3.0 from https://github.com/nddrylliog/greg

support ~{} errblocks
fix "off-by-two" G->text buffer reallocation bug ( Ali Rantakari <visit-with-web-browser@hasseg.org> )
add yyinit yydeinit and pass YY_INPUT G->data Onne Gorter <onne@onnlucky.com>
make C++ compileable Onne Gorter <onne@onnlucky.com>
YY_BUFFER_START_SIZE can be set to change the initial buffer size for parsing
Added offset member in GREG structure
Now every action function (the code between {}) has an additional parameter available: thunk

Add more yyqq cases \a\b\v\e\f.
greg: refactor yyprintcontext (for yyDo), add name to yythunk (for ->action)

revert DEBUG_PARSE_VERBOSE back to DEBUG_PARSE | DEBUG_VERBOSE
free temp context string.
greg -DP: single-line yyDone context
greg -DP only if verbose: single-line yyDone context
bootsstrap greg 0.4.4 from tools/greg.greg (better error reporting)

Fix newly detected syntax error in syntax.y: $ sig
greg-0.4.5: add yyerror, add filename, input, lineno

add YY_ERROR(G, message)
revamp YY_INPUT (G as first arg)
use G->input as new default input stream for YY_INPUT and YY_ERROR
initialize input, filename, lineno in parse_new
add filename to potion_parse for diagnostics
yyqq: escape % to %%
remove undeclared and unneeded GREG* from yyprintcontext
define DEBUG_PARSE, DEBUG_VERBOSE for YY_DEBUG (tested ok)
use YY_ERROR in potion
add freeRules in parser

add Node Variable
rename greg.greg to greg.y
greg YY_DEBUG: support greg -vv (more verbose)