Update for new glib::Value::get signature

[fengalin]

... in consequence of gtk-rs/glib#513

For the Result<_, _>::expect behaviour, please see the following discussion: gtk-rs/gir#825 (review). TLDR: the argument for expect should refer to the context (or the reason why it shouldn't panic), the error will be automatically added in the panic message (using the Debug trait unfortunately).

For the method names, please see: gtk-rs/glib#513 (review) and then gtk-rs/glib#513 (comment). TLDR: get allows writing generic code, get_some is the best name we could think of to get the actual value for a non-optional Type without the need to unwrap an Ok output of get.

[EPashkin]

Please, repase it to pending branch and Edit PR

[EPashkin]

@fengalin Thanks

[fengalin]

\o/

[sdroege]

@GuillaumeGomez looks all good now :)

[GuillaumeGomez]

Indeed! Thanks @fengalin !