choc_WebView.h missing <functional> (minor issue)

[Dana Batali]

Minor issue: compiling trivial example which includes "choc/gui/choc_WebView.h" fails with:

choc_WebView.h(92): error C2039: 'function': is not a member of 'std'

Simple workaround is to #include <functional> prior to webview, but choc_WebView.h (and others perhaps) should include it.

The example test (main.cpp) hides this issue because it includes the kitchen sink (via choc_tests.h).

[Julian Storer]

Thanks! I've pushed a fix for that now