lowercase module name

[balboah]

Breaks builds on non-windows,

parsing go.mod: unexpected module path "github.com/Microsoft/go-winio"

Fixes #156

[noxer]

The problems occur on case sensitive file systems. Some of the microsoft packages use package names with Microsoft, some with microsoft which also leads to problems when modules are vendored on one file system and then copied to another one.

[TBBle]

I feel like this change would needlessly break users who are using github.com/Microsoft/go-winio as an import correctly, instead of trying to go via github.com/microsoft/go-winio as seen in #156.

[kevpar]

I agree that this would be too disruptive to existing users to change the module name to lower-case. I think a good change to improve the state of things would be to add a canonical import path of github.com/Microsoft/go-winio to the files in this repo.