Add Linux 32-bit library
I can't run pyxel on linux 32bit because "libpyxelcore.so" is for 64bit system.

```py
[...]
File "/usr/lib/python3.7/ctypes/__init__.py", line 356, in __init__
    self._handle = _dlopen(self._name, mode)
OSError: /usr/local/lib/python3.7/dist-packages/pyxel/core/bin/linux/libpyxelcore.so: wrong ELF class: ELFCLASS64
```
Can you add library for Linux 32-bit system?