Rename signin to make it more discoverable

[laedit]

I am developing a new konnector for Gaz de Strasbourg and since it is heavily based on old ASP.NET form navigation, I use signin to submit the form for each navigation.

In order to help everyone realize that signin isn't just for authentication, I think that it should be renamed like submitForm, or at least exposed under two names.

I can propose a PR if you are ok with the idea.

[doubleface]

I like the second solution with two names. submitForm is OK for me.

I think you can do your PR, thanks 👍 !