fix arguments getting in mrb_uv_fs_write
replace error message with uv_strerror
create method to clear temporary file used in tests
use test_str variable in test
use uv_buf_t to pass memory range
update libuv version and add notice about it in README
Merge pull request #24 from take-cheeze/refactor

Refactor and libuv update.
update and support libuv-0.11.22
Merge pull request #25 from take-cheeze/libuv-0.11.22

Update and support libuv-0.11.22.
Fix build