Fix unexpected behavior with break

Remove needless MRB_API

```
def yie
  yield
end

def bre
  yie {
    1+1
    break
  }
end

p bre #=> display 2, but should be nil
```

ref #3215

If a function (such as mrb_read_irep_file()) is declared without MRB_API
in header file (such as include/mruby/dump.h), implementation of the
function in source file (such as src/load.c) should also defined without
MRB_API.

If MRB_API is mismatch, Visual C++ reports link error with C2375 error
code: https://msdn.microsoft.com/en-us/library/5k6kw95a.aspx

Visual C++ support of UTF-8 hack on mruby-print

Accept @mattn's comment.

Fix a couple typos in limitations.md

Fixed regex order falling early in arch cases, causing x86_64 and arm…

Re-written android.rake task for latest Android NDK clang. Currently …

Re-written android.rake task for latest Android NDK clang. Currently loses support for GCC and mips, mips64. Addresses issue #3208

Fix SEGV when splat object

Splat operation should return an array.
And raise an error if result of convert by to_a is not array or nil.

surpress warning when MRB_DISABLE_STDIO

Fix SEGV when unshared env

Should clear method name

- Fix method name in top-level
- Fix SEGV when call Exception#backtrace if callinfo over CALLINFO_INIT_SIZE(32)

In mrbgem_spec.rake, added support for @mrblib_dir @objs_dir, so that a gem can have custom source directory names

Fix mrbc_filename leak

In mrbgem_spec.rake, added support for @mrblib_dir @objs_dir, so that a gem can have custom source directory names

instance_eval env should remake Fix #3191

Add new test for optimize VM

To avoid VM nesting with mrb_funcall()