Simplify jar overloading by permitting string inputs

[alanbixby]

To overload jar, you need to pass an object { session: 'COOKIE' }, this is not intuitive and results in over complicated looking code.

await noblox.getCurrentUser({ jar: { session: 'COOKIE' } })
// is now equivalent to
await noblox.getCurrentUser({ jar: 'COOKIE' })

This pull request removes the need for the session object, enabling a cookie string to be passed instead of the wrapper object- backwards compatibility is maintained.

---

string and object (str) highlight the new functionality

[alanbixby]

When making the test case screenshots I also noticed getCurrentUser() is case-sensitive, so I slapped a quick filter in to patch that too.

await noblox.getCurrentUser()
await noblox.getCurrentUser('UserName')
await noblox.getCurrentUser('uSeRNaME') // <- used to return undefined

OLD:

NEW:

[Neztore]

I initially had reservations as this would not play well with setting session_only to false.
As it turns out, setting session_only to false is broken in the current version of the library anyway - is it worth supporting going forward? I think this change is fine and simplifies authentication in a way which is closer to what we want