Update to Cython 0.25.2.

Fix Certificate Transparency support causing some SSL sites fail
to load after some time (#279).

Fix ApplicationSettings.cache_path not working (#283).

Fix: Not a clean shutdown in examples, when closing app while browser
is still loading a website (#282).

Fix loading local filesystem urls that contained any of ? & =
characters (#273).

Fix Request.SetPostData and GetPostData segmentation faults (#228).

Add ApplicationSettings.net_security_expiration_enabled.

Update ExecuteJavascript docs with scriptUrl="" and startLine=1
default params. Also worth noting that ExecuteJavascript crashed
in earlier CEF versions when startLine wasn't provided or was <= 0
(Issue #268).

Add a test that measures execution time for calling Python function
from javascript and then js callback.

Add Contributing guidelines / Issue template.

Update automate.py, include ceftests executable.