Add target_hint to BrowserOptions

[Azorlogh]

See #44

[amodm]

Given the test failures, I think it's best to move BrowserOptions to a non-consuming builder pattern. This way devs can selectively override the specific options they want to override

e.g. instead of saying BrowserOptions { ... }, it should be something like BrowserOptions::new().with_target_hint("_self"). If you're unsure about it, allow me to make changes to this PR so that I can get the tests to pass.

[Azorlogh]

I changed it to the non consuming builder pattern & fixed the rustdoc. Feel free to make edits if necessary

[amodm]

Thanks for your first contribution here @Azorlogh. This will go out in the next release (ETA 2-3 days), after I've had a chance to see if anything else needs to be included in the release. Will tag you when the release is done.

[amodm]

@Azorlogh this is now released as v0.7.0

[Azorlogh]

Awesome, thanks!