Adding windows support

[strangebug]

Hi,

First of all, great work 👍

I was wandering if you would consider a PR or making a few modification to add windows support. Actually, it almost support compilation on windows right off the bat. The only thing preventing it is a unix syscall in segment-readonly.go.

	if unix.Access(cwd, unix.W_OK) != nil {
		p.appendSegment("perms", segment{
			content:    fmt.Sprintf(" %s ", p.symbolTemplates.Lock),
			foreground: p.theme.ReadonlyFg,
			background: p.theme.ReadonlyBg,
		})
	}

So I made the modification

	const W_USR = 0002
	// Check user's permissions on directory in a portable but probably slower way
	fileInfo, _ := os.Stat(cwd)
	if fileInfo.Mode()&W_USR != W_USR {
		p.appendSegment("perms", segment{
			content:    fmt.Sprintf(" %s ", p.symbolTemplates.Lock),
			foreground: p.theme.ReadonlyFg,
			background: p.theme.ReadonlyBg,
		})
	}

and it seems to work just fine (at least if you're using git-bash).

I made the change by adding a specific implementation for windows so I'm sure it doesn't break anything for Unix users. But it's not really necessary, what's your thought about that ?

It is not thoroughly tested but I don't mind testing some more and submit a PR ;-)

More details

[strangebug]

After installing a proper font from https://github.com/powerline/fonts. No more glitches ;)

[justjanne]

Could you open a Pull Request for this?

[strangebug]

Sure, done.