Add mail endpoint examples

[hkraal]

In the YC118.8 relase on September 15th a new CREST endpoint has been added (/characters//ui/openwindow/newmail/). It would be nice to have some examples in the documentation.

Source: https://developers.eveonline.com/blog/article/yc118.8-crest-features

[jonobrien]

it would be nice to have examples of all the endpoints, are you talking just documentation, or pycrest usage?

CREST 3rd party Documentation is over here although the mail endpoint is not documented there either, you could PR that json if you want.