Not create local variables in scope_new
Merge pull request #2419 from santazhang/use-const

add a few const qualifier
Merge pull request #2420 from ksss/reduce-lv

Not create local variables in scope_new
Proc#arity return 0 when opcode was not OP_ENTER
Merge pull request #2421 from ksss/safe-arity

Proc#arity return 0 when opcode was not OP_ENTER
proc.h: MRB_ASPEC_REST() macro return 1 or 0

MRB_ASPEC_REST() is macro just only checks whether truthy or falsy.
And truthy means exist 1 rest argument in current proc.
OP_ENTER: Rewrite split aspec use macros
Merge pull request #2422 from ksss/aspec-macro

OP_ENTER use MBR_ASPEC_* macros
Implement Proc#parameters
Add documentation of `mrb_value` config.
Add notes about restriction of `DISABLE_STDIO`.
Merge pull request #2425 from take-cheeze/mrbconf

Update mrbconf.
Merge pull request #2423 from ksss/proc-parameters

Implement Proc#parameters
Merge remote-tracking branch 'upstream/master' into ext