area of implicit nil is not enough to nregs

Define eval as module function.

correct to compare MRB_STACK_GROWTH.

Refactor numeric.c

Refactoring Comparable

Add Array#keep_if

Use mrb_int in mrbgem rest arguments getting.

Fix MSVC warnings for error.c

Support file name and line number argument in eval.

RRange excl flag use mrb_bool insteard of int

Refactoring OP_CALL

Refactoring Array#__svalue

Only a nil binding will be supported.

By reordering parsing string with mrb_parser_parse won't always start with line 1.