Merge branch 'webview-js-retval'

Integrate GSoC 2017 work by Jose Lorenzo on allowing returning values
from JavaScript code via wxWebView::RunScript().

docs/changes.txt

@@ -105,6 +105,7 @@ All:
 
 All (GUI):
 
+- Allow wxWebView::RunScript() return values (Jose Lorenzo, GSoC 2017).
 - Allow using fractional pen widths with wxGraphicsContext (Adrien Tétar).
 - Improve wxSVGFileDC to support more of wxDC API (Maarten Bent).
 - Add support for wxAuiManager and wxAuiPaneInfo to XRC (Andrea Zanellato).