MSVC: include float header for _isnan and _finite
Update Array#each to be slightly faster.
small refactoring for Array#each
prototype refactoring on mrb_load_irep(); close #647
Fix document. (Use minirake instead of make.)
Modify String#bytes.

It should return non-negative integer.
Add makefile for backward compatibility of shell build processes.
update INSTALL document based on #650; according to #651
possible to specify ENABLE_GEMS=true.
replace "minirake" to "ruby minirake" for non UNIX platforms
add 'default' task if not specified.
add mrb_mod_cv_get
add mrb_cv_get
mrb_mod_cvar_get
add check_cv_name
add test for Module#class_variable_get
refactor mrb_vm_cv_get
add mrb_mod_cv_set, mrb_cv_set
Allow COMPILE_MODE to be changed from ENV
Prettify Rakefile