Add Module#class_variable_get for mruby

add 'default' task if not specified.

possible to specify ENABLE_GEMS=true.

Fix document. (Use minirake instead of make.)

Add Makefile for backward compatibility of shell build processes.

Modify String#bytes.

It should return non-negative integer.

Slightly faster Array#each method.

MSVC: include float header for _isnan and _finite

fix memory leak in function: make_cdump_irep

Derive DISABLE_GEMS macro according to build configuration

refactoring src/dump.c

add AR, YACC flags.

fix build

GEMS.active support relative path

minirake exit status not 0, when build failed.