define and use print format macros for mrb_int

For portability: %ld can't be used to print a 64-bit mrb_int on
WIN(32|64) because long is 32-bit wide.
Optimize OP_ADD instruction.
Optimize OP_SUBI.
Remove mrb_checkstack() as unused.
Make some tiny functions inlined. This is for supeed tuning.
Extract uvget/uvset to OP_GETUPVAR/OP_SETUPVAR. This is for speed tuning.
Make topenv() inlined.
Clean some redundant code up.
Lazy variable declarations. They are for speed tune.
Simplify conditional expressions. This is for speed tuning.
%I %i literal
implement literal %W %w %s
refactor string parsing
Could you add me to AUTHORS?
refactor heredoc identifier
remove disused check code
bugfix about escaping '\n'
remove unused local variable beg in parser_yylex
Add new API mrb_true_or_false_value().
Remove the macro mrb_bool_value(). Use mrb_true_or_false() instead.
Use mrb_true_or_false_value() / in mrb_struct_equal().