use mrb_str_cat_lit for literals

use NAN and INFINITY macros

Make type casts safer

fix #1823

The macro str_to_mrb_float (strto[df]) converts a string to a number,
but these two macros can be used to directly get the special value.

The NAN macro requires quiet NaN support, but so does str_to_mrb_float.

This change also circumvents missing C99 support in Microsoft's C library.
Its (or ISO C90's) strtod doesn't parse "nan" or "inf".

Use sizeof(void*) instead of mrb_int size and extend embed string size.

two pool fixes

support linenoise in mirb

C4146 (unary minus operator applied to unsigned type, result still
unsigned)

Embed small string

.PHONY should be placed after `all'

Fix behavior Hash#eql?

Because some make (e.g. nmake) recognize it as a normal rule definition and if it's the first rule, make runs it as a default rule.
Consequently `all', `test' and `clean' are all ran (because they are depended by .PHONY), and builded files are cleaned.

use flags 4 for *this object is embed*
use flags 8~64 for *embed string length*

Fix build on mingw32

fixed broken gettimeofday implementation for Windows

small, but critical typo :)

Fix and add test for Proc#source_location.

visualcpp toolchain: change compiler/linker flags