Fix MSVC errors

[shohirose]

I made several changes to your library. I hope these changes improve your code.

The reasons of the 2nd commit about /utf-8 and /EHsc are

• Because compiling lexy with MSVC requires utf-8, it is natural to add /utf-8 option to lexy_dev itself.
• When opening the root directory with Visual Studio, VS does not automatically add /EHsc option, leading to a compilation error. (This does not occur when using VSCode.)

[foonathan]

Thank you!