feat(path/glob): add caseInsensitive option

[lowlighter]

Closes #806

This add a caseInsensitive option to globToRegExp.

When os option (which defaults to current os) is set to "windows", this option will be enabled by default as file system is case insensitive on it

[piscisaureus]

I'm not convinced 'caseInsensitive' should be enabled on windows by default.

• Users might be tempted to think that glob will do case folding exactly like windows, which this doesn't.
• With the advent of WSL there are now case-sensitive directories on my windows box.
• On mac, we don't perform unicode normalization either.

I think it'd be better to make the default 'case sensitive' everywhere, and make windows users think about it a little harder.

[lowlighter]

I think it'd be better to make the default 'case sensitive' everywhere, and make windows users think about it a little harder.

Yes. I changed it to default it to false on all platforms

[kt3k]

LGTM