let the C compiler validate the identifier

remove mrb_define_method_vm() function

Update Coopyright Information to year 2015

Some C compilers may allow other characters in identifiers such as $.
They may also implement C99's extended identifiers (\u30EB\u30D3\u30FC,
ルビー).

It isn't needed as it's very similar to mrb_define_method_raw() and also
there's only one place where mrb_proc_ptr() actually has to be called.

Inspired by @furunkel's method cache patch (#2764).

Reenable mrb_dump_irep under DISABLE_STDIO.

remove unused token declarations

Avoid unnecessary stores and reloads

Remove INSTALL and improve README instead

fix splat without assignment

The parser generates NODE_NIL for tSTAR without argument in masgns. The
codegen didn't handle that.

define YYDEBUG macro conditionally

Defining static version of frexpl also fro MIPS platforms.

On MIPS/linaro, libm.so lacks frexpl() as CygWin does.

The YYDEBUG macro enables parser debugging which
unnecessarily increases the executable size (9 to 10 KB).
Now it only will be defined when PARSER_DEBUG is too.

src/load.c: fix size error macros

parser: fix possible null dereferences

prevent accidental macro redefinition of strndup()

mrb_read_irep_file(): unify error handling / fix uint underflow

Previously there wasn't a way to trigger the useful definition, but it
is needed and that in every case to check for integer overflow due to
multiplication and faulty/modified binary files.

Also change existing code to a calloc()-like parameter order.

It's only used once and in that case it isn't necessary anyway, since
size_t must be at least 32 bits wide and
the max. length of a filename is UINT16_MAX.

parser_state->locals might be a null pointer.

Fixes (and other similiar invalid code):
def a; Proc.new do def x==x end end

buf_size has to be greater than header_size, otherwise subtracting
header_size from buf_size will cause an integer underflow.

Being equal to header_size is fine, however useless, so quit early.

Convert mrb_read_irep_file() to use goto like read_section_lv() and
read_section_debug() already do.

Fix misspellings in document

Add rake task for benchmarking