Add #file_exists? Top-level Macro Method

[toddsundsted]

Useful when composing the name of a file to read from in a macro.

I use this in my Kemal applications to create a render helper that takes a file name and checks for various flavors of templates using the name:

render "objects/index" # checks for and renders index.html.ecr, index.html.slang, etc.

The alternative is to use #read_file? as a check for existence. (Maybe there's another way that I'm missing.)

[straight-shoota]

Could you please open an issue as feature discussion first? It can reference this PR. But this helps to keep general discussion of the feature separate from implementation details. Thank you.
It would be great to show how this improves code compared to #read_file?.

[Sija]

Aside of the more substantial arguments that method should be called sth like file_exists?, since exists? is too generic for a top-level method.

[toddsundsted]

good suggestions! done!

[straight-shoota]

If you would rename the macro to file_exists?, I think this is good to go.

[toddsundsted]

@straight-shoota done!